Cut off the outer edge of each tortilla and remove so that the tortillas fit snugly into the muffin tin cups. Brush both sides of the tortillas lightly with the melted butter and sprinkle with salt. Press the tortillas into the muffin tin, creating little tortilla cups.
In a small bowl, mix half the salsa with the black beans and season with salt and pepper. Spoon a heaping tablespoon of the black bean mixture into each tortilla cup. Crack an egg into each of the eight cups. Bake until barely set, about 8 minutes. Top with cheese, cover with aluminum foil, and then bake for 6 to 7 minutes more. To serve, spoon the sour cream and remaining salsa on top of the eggs.