In a medium saucepan combine margarine or butter and half-and-half, light cream, or milk. Cook and stir until margarine or butter melts. Add packed brown sugar; stir until sugar dissolves. Remove from heat.
Stir in chopped pecans or walnuts and flaked coconut. Spread over warm cake (in metal pan). Broil about 4 inches from heat for 2 to 3 minutes or until topping is bubbly and golden. Makes enough topping for one 8- or 9-inch one-layer cake (9 servings).