Rinse and drain beans thoroughly. Place them in a large saucepan or soup kettle and add all remaining ingredients. Bring to a boil, reduce heat, simmer, uncovered, for 1 1/2 hours.
Remove and discard ham hock and bay leaf. Using slotted spoon, transfer bean mixture, in batches, to the bowl of a food processor. Process, adding cooking liquid as necessary to form a smooth, thick paste. You will use a total of about 1 cup liquid.
Transfer the pesto to a bowl and stir in the salt and pepper if needed. Refrigerate, covered, until ready to use. Will keep in fridge for 2-3 days.
Preheat oven to 375F. Fill a heavy skillet with 1/2″ corn oil. Heat it until oil just starts to move. Then fry the tortillas, one at a time, until light golden brown, about 15 seconds on each side. Drain on paper towels.
Slice chorizo into 1/4″ thick rounds and saute them in a small skillet until crisp, about 5 minutes. Remove sausage from skillet and drain on paper towel.
Place tortillas on baking sheet, and spread pesto evenly over them. Arrange sausage over pesto and sprinkle with cheese. Top with chopped cilantro.
Bake until brown, 20 minutes. Remove from oven and cut each tortilla into eight pieces. Serve immediately.