Combine 2 cups of the beans with the pepper, onion, garlic, cilantro, cumin, and salt in a large bowl. Puree the remaining 1/2 cup of beans with the egg white in a food processor. Mix the puree into the other ingredients, vigorously mashing it all together (it’s very satisfying to use your hands for this step). Sprinkle the cornmeal over the black bean mixture and work it in. If it seems dry, add a little water, 1 tablespoon at a time.