Step 1

Reconstitute the corn husks.

Step 2

In a small saucepan, combine the black beans, avocado leaves, lard, onion, and 3 cups water. Set saucepan over high heat. Bring the liquid to a boil. Reduce the heat to medium-low. With lid slightly ajar, simmer until the beans become very tender, about 1 1/2 hours. Add additional water as necessary if the beans begin to dry out during the cooking process.

Step 3

Remove and discard the avocado leaves from filling. Generously season filling with salt. Remove pan from heat, and set the filling aside to cool.

Step 4

Using a potato masher or a large spoon, coarsely mash the filling until it becomes thick enough to easily hold its shape when placed in a spoon.

Step 5

Assemble 16 tamales with the tamale batter and the black-bean filling, using large husks for wrappers and ties, and reserving smaller ones to line the steamer basket and cover the tamales.

Step 6

Prepare the steamer, and steam the tamales. Let the tamales stand until the batter has firmed. Serve the tamales warm with the chopped-tomato-and-serrano salsa.