Preheat oven to 375 degree F. In a medium skillet cook onion in hot butter about 5 minutes or until just tender. In a large bowl stir together corn muffin mix, egg, water, applesauce, sour cream, cheddar cheese, snipped sage leaves, and a few dashes pepper. Stir in onion mixture. Pour mixture into a 2-quart square baking dish.
Bake for 25 minutes. Brush apple slices with melted butter and arrange on top of spoon bread. Bake 25 to 30 minutes more or until spoon bread is golden brown across the top. Let cool in pan on a wire rack for 15 minutes before serving; spoon bread may sink slightly in center while cooking. Sprinkle on sage leaves before serving. Makes 8 servings.