In a bowl, combine the cornbread mix, milk, oil and egg. Spread in a greased 9-in. square baking pan. In another bowl, combine the onion, corn, 1 cup cheddar cheese, sour cream, mayonnaise, salt and hot pepper sauce.
Spoon over batter. Top with remaining cheese. Bake at 425° for 25-30 minutes or until golden brown. Cool for 15 minutes before cutting. Refrigerate leftovers.