In a skillet saute onion in butter until tender; set aside.
In a large bowl, beat the egg; add sour cream, both the corns, salt and pepper. Stir in the corn bread muffin mix just until blended. Fold in onions and jalapeno and half of the cheese.
Transfer to a greased shallow baking dish. Sprinkle with the remaining cheese. Bake uncovered at 350° for 30 to 35 minutes or until a toothpick inserted near the center comes out clean. Cool slightly before serving.