Step 1

Heat butter in a large pot over medium. Add bell pepper, onion, jalapeño, and garlic and cook, stirring occasionally, until vegetables are very soft, 10–12 minutes. Add beans and chicken broth. Bring to a simmer and cook, stirring occasionally, until liquid is reduced by half and thickened, 20–25 minutes. Stir in cilantro; season with salt and pepper. Keep warm.

Step 2

Pour oil into a small skillet to come ¼" up the sides. Heat over medium-high until very hot. Working one at a time, fry tortillas until lightly browned and very crisp, about 1 minute per side. Transfer to paper towels to drain.

Step 3

Melt 1 Tbsp. butter in a small nonstick skillet over medium heat. When butter begins to foam, add 3 egg whites and a pinch of salt and cook, stirring constantly with a rubber spatula and forming a compact bundle, until whites are set but still moist, about 1 minute. Transfer to a plate. Repeat with remaining 1 Tbsp. butter and 3 egg whites.

Step 4

Divide sour cream between tortillas. Top with ½ cup bean mixture, followed by lettuce, egg whites, a drizzle of hot sauce, cheese, avocado, and cilantro.