Preheat oven to 350 degrees. Mix together room temperature butter with the cake mix, either by hand or pastry cutter, until crumbly. Mix in coconut. Press in bottom, and slightly up side of ungreased 13x9 glass pan.
Bake 10 minutes. While baking, toss apples with cinnamon and sugar. In a separate bowl, combine egg and sour cream.
Arrange apples over warm crust when removed from the oven. Spread or drizzle sour cream mixture over the apples. It may not cover them completely, but that is fine. Bake 25 minutes until crust is starting to turn golden brown.
Serve warm or cold, as is, or with vanilla ice cream or homemade whipped cream! Enjoy!