Melt the margarine in a skillet and saute the onions until tender. In a bowl combine the sour cream, salt, parsley and 1/2 cup cheese. Combine and add to the onion mixture and set aside. Combine the muffin mix, egg, milk, corn and hot sauce and mix well. Spread in a greased 9 x 9 inch pan. Cover with the sour cream mixture. Top with the remaining cheese. Bake in a 425 degree oven for 25 to 30 minutes