Step 1

To toast the tortillas in the oven: Preheat the oven to 375 degrees F. Spread the tortillas on a baking sheet. Bake for 10 minutes, or until crisp and dry and just starting to be touched with golden brown spots. Remove them from the oven and place on a serving platter.

Step 2

To toast the tortillas on a stovetop: Heat a large skillet. Toast the tortillas over medium heat (two or three at a time, depending on the size of the skillet) for about 5 minutes or so on each side, until crisp and touched with golden brown spots. Don't be afraid to let them get nice and crisp—that's better than ending up with a soggy tostada.

Step 3

Heat the oil in medium skillet. Add the onion and garlic and sauté until golden, about 5 minutes.

Step 4

Add the remaining ingredients (aside from the garnishes, of course) along with 1/4 cup water and bring to a simmer. Using a potato masher, mash some of the beans so that the liquid becomes thick and saucy.

Step 5

Place the shredded lettuce, sour cream, and salsa in separate serving bowls and let everyone assemble their tostadas as follows: A layer of shredded lettuce; the black bean mixture; salsa; and sour cream. Pick up the tostadas and eat out of hand (with plenty of napkins!).