Preheat oven to 350 degrees. Place pecans and coconut in the bottom of a sprayed 9 by 13in baking pan. Combine cake mix, 1 1/2 cups of water, oil and eggs in bowl and beat well. Carefully pour batter over pecans and coconut.
Combine butter, cream cheese and powdered sugan in bowl and whip to blend. Spoon mixture over batter and bake for 45 minutes. The icing sinks into bottom as it bakes and forms a ribbon inside. You can't test doneness with a toothpick in this recipe, because cake will appear sticky, even when done.