I can't find where I got this recipe or I'd give credit but it was posted on a blog last week...I could literally eat this whole cake/pie in one sitting. I've seen many more complicated recipes, but after you try this one you will never need them.
Yellow Cake mix - plus ingredients to make - eggs and oil
1 pkg instant vanilla pudding
1 1/2 cups cool whip
1 cup cold milk
1 block unsweetened baker's chocolate
1 T butter
3/4 cup powdered sugar (I think I used more like 1 cup
3 T cold milk
Bake cake mix as directed in 2 round pans. I prefer Duncan Hines. Let cool.
Filling: Mix pudding and milk for 1 minutes and then stir in coolwhip. Spread between two cake layers.
Melt chocolate and butter in the microwave. Add powdered sugar and milk until smooth and spread on top layer of cake immediately.
Refrigerate cake...and enjoy!