Sammy Sosa leans over confidentially. "It was a special treat for the king. For the Aztec king. Ordinary people couldn't eat it."

I look at the black morass on my plate. I almost expect him to take it back and say, "Sorry, you don't qualify."

Instead, he says, "Buen provecho."

"Is this the real thing?" I ask.

"The real thing," Sammy says.

Great, because that's what I've been searching for. Serious mole. That's "molay," the sauce, not the black-eyed burrower working beneath suburban folks' rose gardens.

I've found this ancient Aztec food here at La Espadaña ("the bell wall"), in Tijuana's Rio district: mole poblano, the most famous of them all, with chicken enchiladas. Hey, near enough to September 16. Mexican Independence Day. Happy birthday, Mexico!

Sammy's the real thing too. That is, his name really is Sammy Sosa. Okay, he never whacked balls for the Chicago Cubs. But he's been a waiter here at La Espadaña so long, you know he knows how to whack a mole together.

Searching for the perfect mole is like searching for the perfect chocolate chip cookie. Mole's an icon in its own right, the way curries are to Indian cooking, or olive oil to the Mediterraneans: it's one of those definers of culture, and an open telephone line back to the Aztecs. Of course, this mole is a southern-central Mexican thing, a lush, oozing accompaniment to chicken or turkey or pork, lifted from jungle kingdoms dripping with plantains and chocolate trees and mangos and other rich sauces. It's not like the tart, crackling-hot rattlesnake 'n' scorpion dishes of Sonora and Baja. You don't hear a lot about mole up here in the desert north.

"Mole" comes from the Náhuatl word milli or molli, which means "sauce" or "concoction." But people talk about it in almost mystical overtones. 'Specially mole poblano. It seems to be not just the best known but the Cadillac of moles. To many, even up here in Tijuana, mole poblano over turkey (mole de guajolote) is the national dish, eaten, since Spanish times anyway, at Christmas.

"It's the soul of Mexican sauces," Alberto Mondragón, the manager of El Agáve restaurant up in Old Town told me the other day. "It's sweet, spicy, and rich. Drink plenty of water with it. Don't eat it early or late. It's richer than other sauces. You need time to digest it."

He takes the tradition seriously. "Mole is for Mexican cuisine what baroque art is for architects," Mondragón writes on his menu. I'd love to eat at El Agáve, but it's a little on the "up" side for me.

So here I am, sitting at La Espadaña, down on Sánchez Taboada Avenue in the Rio district. It's about six in the evening. Plenty of time to digest. Nice place, too. La Espadaña is where local government officials meet, business people, families, the middle class. It's like a bright ranch house inside, with a low-sloped rafter roof, a campestre (a bell tower, with ropes you can pull when you have something to celebrate), orange walls, arched alcoves for intimate eating, lots of interesting Talavera pottery, and against the far, luminous-blue wall, chefs flipping steaks on flaming grills.

So, okay, Sammy, here goes. Big moment. I haul a chunk of enchilada up through the black lagoon of my mole poblano. Send it down the hatch. Wow. Is this what Moctezuma tasted? Rico. My first thought is: distant echo of molasses. Mole. Mol-asses -- coincidence?

Of course, this mole is way richer. It's multilayered, and the more you taste it, the more interesting it gets. That sweet, slightly tarry flavor mixed with...hell, I don't know, but I'd guess banana? Chocolate, for sure, and there's something nutty, chile-hot...

Whatever, it does make the enchiladas delicious. If I was a wine-critic type, I'd say this mole delivers swoony vividness that envelops your taste buds like thunderclouds -- hey, that's good! Of course, you definitely need your iced tea. The rice and frijoles help too.

From the simplified recipes I've seen, this mole will have, at the least, a bunch of chiles, and interesting things like almonds, torn-up corn tortillas, raisins, cloves, cinnamon, and a certain amount of bitter chocolate.

"How much chocolate is in this mole?" I ask Sammy.

"The chef's over there," Sammy says. "You could ask him."

So I do. Carlos Ramírez stands at the open grill station. He's a big man. Been chef here 15 years. "I put in 20 different spices," he says. "I fry them up together. It's in the combination of chiles, nuts, chocolate. You have chile negro, chile pasilla, chile California (the dried red Anaheim chile), creamed peanuts, plantain, piloncillo..." He says piloncillos are cones of solid, raw brown sugar with -- aha! -- a molasses flavor, even though the molasses (the first stage of the process that converts cane to sugar) has mostly been refined out of it.

This is just the beginning. He blends it all with chicken broth, stirs, drains, tastes, seasons. I'm sure he's not going to tell me his secrets. So I don't get how much chocolate, or cacao, is in there. "My recipe is traditional" is what he says.

***

"No, no, no," says my friend Victor a few days later. "La Espadaña's fine, but the best mole in Tijuana is at Herminia Amador's."

So here is your intrepid correspondent, back tramping eastward alongside a dusty railroad track a few hundred yards south and east of the San Ysidro border crossing. It's around five in the afternoon. Behind me, in the shade of the old, unused Tijuana railroad-station platform, men gather at about this time of day to decide whether to try to make it across the line from here after dark. This is Colonia Libertad. So close to the border, yet couldn't be more Mexican. Politicians' banners bleach in the sun and get hazy in the dust. Tiny taco stands pop up in little gardens. Sidewalk comes and goes. Traffic is a bit crazy but kindly to the many walkers, like me.

Avenida Ferrocarril ("Railroad Avenue") turns into a calle, Fourth Street. I realize I'm heading directly back toward the U.S. The road climbs to a black border fence. Beyond, halfway up the bare hills, a second fence plays backup. Then, in the last 100 yards of México, little Avenida Aquiles Serdán tees off to the right. I scan the row of low buildings and muffler shops. Ah. There, next to Radiadores, Mofles Tony, and in the deep shade of a ficus tree, the magic words appear.

"La Casa Del Mole."

I cross the road. This has to be where Herminia Amador created the original Casa. The restaurant has a traditional tile-roof frontage, cream walls, black metal-barred windows. The towering ficus makes it look small. You wonder how anyone ever finds it, hidden behind a black metal security door. And yet the inside tells you they have prospered -- and the clientele is obviously from all parts of town, and across the line too.

Tijuana's love affair with mole is said to have begun right here, 16 years ago. Herminia Amador dreamed of bringing the flavors of her native state of Puebla to Tijuana. That meant one thing: Mole Poblano. The place has done so well, it's spawned three other Casas Del Mole around town, including a new one out at Playas de Tijuana, near the beach. This original restaurant is used but confident, comfortable, a bright interior dressed to look like an old Mexican courtyard. It has a little jungle of flowers and ferns, a gurgling fountain, yellow stucco walls with brown highlights, a tile "roof" overhanging the open kitchen, arches decorated with false cherries on branches, red-tile floor, shiny brown leatherette booths, and piles of thick china plates stacked and ready for the customers they know are coming tonight.

Prisciliano Camacho Flores turns up with a menu. "Our founder, Herminia Amador -- unfortunately, she passed away last October -- she was from the state of Puebla. Mole 'poblano' means 'from Puebla.' That is our full name. 'La Casa del Mole Poblano.'"

They have plenty of choices, but really there is only one decision you have to make. What's going under your mole? Thigh or breast of chicken or three enchiladas?

I choose the breast of chicken, which comes after a tasty chicken soup (included in the reasonable price, as is a sweet tamal dessert). Somewhere under this beautiful-smelling browny-black gloop, a chicken's hiding. You chomp into your first bite. And -- is it that I know better what to look for? This mole tastes less sweet, more complex, nuttier, more pointed, deeper, and perhaps cruder. For sure, it fits the casera-style feel of the place. And, actually, I like it better. Oh, and on top, some ajonjolí -- sesame -- seeds provide a neat little counter-punch for your tastebuds. I guess if you think of the French, with their béarnaise, and the Italians, with their marinara, we're probably looking at Mexico's major sauce statement.

It turns out that they don't actually make the mole here. "We make it for all our restaurants at our Zona Rio restaurant," says Prisciliano. "One woman works full-time making moles."

***

I'm hooked now. A few days later, my friend Hank and I swing up Paseo de los Héroes in a libre taxi, past the massive statues of Cuauhtémoc, Lincoln, and Zaragoza, the Mexican general who defeated the French on Cinco de Mayo, 145 years ago. And right by Zaragoza we come across an eight-sided building with a small sign outside. It's La Casa Del Mole's flagship restaurant, light-years in atmosphere from their original place by the border. Customers sit in galleries around a massive volcanic rock-pile waterfall surrounded by lush plants and what look like real palm trees -- the trunks are real, the fronds are real, but the fronds have been cut from other trees and stuck in. On the walls, an artist has painted eight-foot-tall lilies and sunflowers. Even the tabletops have been painted with flower decorations. But the thing everybody notices is a giant ceramic yellow-brown olla -- pot, bowl -- next to the cashier. The thing's five feet across. They say it's a traditional container from Puebla for the making of mole. True mole, they say, should be made in ceramic. Making it in metal containers is bad for the stomach.

Don't ask me why, but I believe them. This time, I'm determined to try a different mole. After all, Alberto Mondragón had told me they had the six basic moles back at El Agáve in Old Town -- poblano (made with ancho chiles -- which are dried poblano chiles); rojo (red), with a tomatoey flavor; rosa de Taxco (a sweet mole made from beets, walnuts, pine nuts, and chipotle chile); coloradito, a cinnamony mix with banana, garlic, and chocolate; verde, a green Oaxacan sauce mainly colored and flavored by the tomatillo; and negro, a spicier, less sweet Oaxacan mole that sounds a bit like the poblano, with things like fried plantains, almonds, tortillas, chipotle, peanuts, and a bit of chocolate all ground into the mix.

Sigh. Not quite the same choice down here. Ricardo, the waiter, explains that, apart from poblano, they have two other moles today, verde and ranchero, both Oaxacan. He brings out half a dozen dollops on a plate so we can sample them. There's mole poblano, mole almendrado (it's a lot like mole poblano, topped with ground almonds), mole ranchero (brown red chile mole), and a tomatillo-based mole verde. The other two are regular salsas.

I order mole verde with pork chunks. Hank orders chicken breast poblano. And while we're waiting we hop up to the kitchen.

"Sure," says the manager, Margarita Martínez, when I ask if we can see where the mole is made. She leads us out through the kitchen to a building across a courtyard. Inside, Margarita Sanchez labors behind three three-foot-high cauldrons bubbling away on a stovetop. Her work tables are stacked with piles of nuts, beans, almonds, fruit, and chiles.

"It takes me three days minimum to make a batch of mole poblano," Margarita says. "I put 30 to 100 ingredients in. I make three of these ollas each week."

Holy mole. That's a lot. And, looking at Margarita, who's probably in her 40s, solid-set, strong, handling the big pots, sacks, herbs, chiles, liquids...all to get a recipe right that has been perfected over centuries, you feel again that weird link: you imagine priests and soldiers in, say, 1700, fresh off the galleon from Spain, witnessing the same scene. Not to collapse into clichés, but Margarita's our contact with the past.

And in that past, I think I see, this mole was probably looked on as concentrated goodness, the bringing together of all the best, the most exotic of nature's offerings into one magical health concoction, love potion, taste sensation. For the rich and powerful only, of course.

"People have always made mole in large amounts," Margarita says. "It is so much work, you may as well make as much as you can at a time. You have to be exact, but also, down in Puebla and Oaxaca, everybody has their own mama's recipe."

So, who invented mole poblano? Are we eating a Spanish colonial dish or an Aztec classic?

The jury's still out.

Dave DeWitt and Nancy Gerlach, in The Whole Chile Pepper Book, say it was the Aztecs who most likely invented mole poblano, long before the Spaniards arrived. After that, seeing that chocolate was traditionally reserved for Aztec royalty and members of the military and religious nobility, the Spanish ruling elites wanted in. "Perhaps Aztec serving girls at the convent gave a royal recipe to the nuns so they could honor their royalty, the archbishop," write the authors.

But more people seem to think mole poblano was in no way Aztec, even though some, maybe most, ingredients are. They call it a Spanish adaptation of foods the Spanish found in the New World, and they pin it down to between 1680 and 1688 at a convent in Puebla de los Angeles, where, one day, Sor Andrea, the sister superior of the Santa Rosa Convent, wanted to thank the archbishop for agreeing to build a convent for her order. So she combined ingredients from the New World with the Old.

Or was it Fray Pascual? Diana Kennedy, who's a well-known expert on Mexican cooking, says the good fray (we'd say friar) was also preparing a banquet for a visiting archbishop. Turkeys were cooking in casseroles on the fire. "As Fray Pascual, scolding his assistants for their untidiness, gathered up all the spices they had been using, and put them together on a tray, a sudden gust of wind swept across the kitchen and they spilled over [into] the cazuelas (casseroles)."

But Michael and Sophie Coe, who are recognized experts on the preconquest Aztecs, say (in their book The True History of Chocolate) that the Aztecs had nothing to do with it. That the idea of using chocolate as a flavoring in cooked food "would have been horrifying to the Aztecs -- just as Christians could not conceive of using communion wine to make, say, coq au vin...the place of origin of the dish and its sauce [is] the colonial Puebla de los Angeles; this beautiful city, unlike others in central Mexico, has no Aztec foundations."

The Coes have my vote, but take your pick. The recipe for mole could be 1000 years old, or only 400. Whichever, that's some cool bit of history you're eating.

We make it back across the courtyard just in time for our moles. Hank gets the best-lookin' dish with his chicken breast mole poblano and almonds. I filch a bit of his mole. Ah yes. Margaritas. Just like in Colonia Libertad. To simplify for us gringos, maybe, they tell us it's essentially made of dark chocolate, chile, and ground-peanut sauce. For me, it's fruity, chocolatey, beautifully hard to pigeonhole, slightly intoxicating. My green mole verde, basically mole without chocolate and with tomatillos, is good, tart, but I wouldn't know it from a salsa verde.

We come out realizing we've got a long ways to go on this. On the other hand, I'm feeling way ahead of what I knew a week ago. I knew only one mole back then: guaca-mole.