Ingredients

1 cup dried black beans (7 oz), picked over and rinsed
1/2 cup chopped white onion (1/2 medium)
2 tablespoons lard or olive oil
1 teaspoon crumbled dried epazote
9 cups water
1 teaspoon salt

Directions

BLACK BEANS:

Bring beans, onion, lard, epazote, and water to a boil in a 3-quart heavy pot. Reduce heat and simmer, partially covered, until beans are tender, about 1 1/4 hours. Add salt and simmer, uncovered, until enough water is evaporated so that liquid reaches just below level of beans, about 30 minutes.

If using beans for omelet filling: Measure out 1 1/2 cups beans with a slotted spoon and 1/2 cup liquid and mash together in a bowl with a potato masher until creamy. Reserve remaining beans and liquid for another use such as black bean soup.

Cooks\' notes:
• To use canned beans, rinse and drain a 19-oz can of cooked black beans. Cook onion in 4 teaspoons lard or olive oil in a small heavy saucepan over moderately low heat, stirring frequently, until softened, 4 to 5 minutes. Stir in beans, epazote, and 1/2 cup water and simmer 15 minutes, then mash.
• Beans, dried or canned, can be cooked and mashed 2 days ahead and cooled, uncovered, then chilled, covered. Reheat before using.

*We prefer Los Compadres brand, available at Latino markets and Rosa Imports (888-377-1032).