Beat egg in mixing bowl with a whisk or fork
Chop onion
Add beans, chilis, bread crumbs, onion, and cheese to the mixing bowl
Mix well
Heat butter and vegetable oil in skillet on medium heat
Drop bean mixture into hot oil in preheated skillet in groups of four spoonfuls
Flatten bean spoonfuls into 1-inch thick patties
Cook for 5 minutes
Flip patties
Cook for 5 more minutes
Serve with sour cream