Heat oven to 350°. Cut butter into dry cake mix until crumbly. Mix in coconut. Pat mixture lightly into ungreased 13 x 9-inch pan, building up slightly edges. Bake 10 minutes. Arrange apples on warm crust. Mix sugar and cinnamon; sprinkle on apples. Blend sour cream and egg yolks or egg; drizzle over apples. It won't completely cover them. Bake 25 minutes, or until edges are light brown. Serve warm. Makes 12 servings.