Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch pan. Peel, core, and cut each apple into 8 wedges. Set aside.
In a medium bowl, combine the cake mix, coconut and margarine until crumbly. Pat mixture lightly into prepared pan, building up the edges slightly to form a crust. Arrange the apple wedges on top.
Mix together the cinnamon and sugar and sprinkle over the apples and the cake mixture. In a small bowl, whisk together the egg and sour cream.
Drizzle over the top of the cake.
Bake in the preheated oven for 35 minutes, or until the edges of the cake are golden and the apples are tender.
