The glass refrigerator case glows mad bright in the front room, lit by a mercury-vapor bulb that makes the lined-up soft drinks phosphoresce, from the painfully orange Fanta to the grass-green, urine-yellow, and candy-apple-red Jarritos, painting rainbows on the faces of three diners who sit right next to the case. At this late hour the back room is occupied by single Mexican men, who perch one per table, nursing beers, as Spanish-language heavy-metal music thumps through the darkened room. Occasionally a campesino breaks into frenzied song, or springs up and dances a quick two-step with one of the short-skirted waitresses.

Better to sit in the front room of East Harlem’s San Francisco de Asis Restaurant— named after the Umbrian saint who befriended birds and other animals—and watch the busy cook at work, turning out the lengthy menu with amazing efficiency. One moment she’s deep-frying the potato-filled flautas ($5.50), flipping the tortilla tubes again and again with a pair of tongs in a cooking vessel that might be a Chinese wok. When the three are done to the color of a worn saddle, she crumbles Cojita cheese on top, then heaps them with salad. It’s up to you to apply one of the sauces from an ornate metal caddy on the table: fiery brown chipotle or mellow green tomatillo.

Another of her masterpieces is the Pueblan mainstay pipian verde con pollo ($9.50). Note that the mole is listed first in the name, and the chicken second, because the plate is mainly a river of pumpkin-seed sauce, cascading around the moist rice and cheese-dusted beans, lapping at the sides of a boiled quarter-chicken of no particular merit. But the sauce ennobles the bird, using it as a blank canvas to paint toasty and earthy flavors. And the weird green color is likely to end up in Marc Jacobs’s fall collection. The only thing that can match the mole pipian, tastewise, is another thick sauce—adobo, as brick red as the pipian is green. Loaded with dried red chiles, it goes best with chunks of fatty pork in the entrée adobo de puerco ($9.25), and the sauce is spicy enough to break out beads of sweat on your forehead.

A real rarity on the menu is cemitas ($7), sandwiches made from round seeded rolls leavened with beer. Though I’ve seen larger ones in Sunset Park, the version at Saint Frannie’s stands out for the quantity of cheese heaped on, serving as a bed for whatever meat you choose. This profound cheesiness makes the vegetarian version, also featuring ripe avocado, a delight in itself. You won’t miss the meat. Other recommendations include huaraches, a fairly recent Pueblan invention that forms fresh masa into a shape inspired by a tourist’s sandal, then uses it as a vessel to be filled with almost anything. One version sluices runny skinless chorizo into the shoe, then tops it with roughage, crema, fresh cheese, and salsa, opposing the blandness of masa with the saltiness of sausage. Others feature long-braised beef tongue, the salted dried beef called cecina, and carne enchilada, little morsels of spice-dusted pork cut from a rotating cylinder that looks an awful lot like a gyro. That’s because the apparatus is, in fact, a gyro, introduced to Puebla by Lebanese immigrants, probably sometime in the 1960s. That’s culinary fusion par excellence.