In a skillet brown the ground beef. Drain off fat. Combine beans, enchilada and tomato sauces in a bowl with minced onion. Set aside 1 cup corn chips and 1/2 cup cheese. Add the remaining cheese and corn chips with the meat to the beans. Stir to blend. Empty into a lightly buttered 2-quart casserole. Bake, uncovered, at 375 degrees F for 20 to 25 minutes or until heated through.
Spread the top with sour cream and sprinkle with the reserved cheese. Ring the remaining corn chips around the edge; return to the oven for 3 to 4 minutes, or until the cheese melts. This will double or triple easily for a large group. May be made ahead and refrigerated.
