Derided by farmers in this country as "corn smut" and the target of USDA eradication efforts, the fungus known as huitlacoche (wheat-lah-KOH-chay) that sometimes forms on ears of corn was prized by the Aztecs and Mayans and is still considered a delicacy in parts of Mexico. Pepito's Deli in Berkeley has perhaps the most diverse menu of any taqueria in the East Bay, and it includes huitlacoche quesadillas. Owner Mariacutea Elena Magana sautes the morsels (taken from a can, fresh ones being available in early summer only) in oil with onion, tomato, jalapeño, and epazote to create a black goo that's served in a flour tortilla with melted Monterey jack. The taste sensation is unique -- robust yet subtle -- and it lingers in the mouth, making you crave another quesadilla hours later. They sell for $2.25 and together with a burrito -- the papas (potato) con chorizo is recommended -- make for a hearty meal. The restaurant doubles as a market, and if you eat there, be careful not to discard your paper plates and napkins in bins that hold bulk dried beans but can be mistaken for trash cans.