In a bowl, combine butter and cake mix until crumbly. In the crockpot, spread the pie filling. Pour the cake mixture over the pie filling. Cover and cook on low for 2 hours.
I sometimes sprinkle cinnamon or nutmeg over the cake mixture. I suppose you could try different variations, like raspberry pie filling and chocolate cake mix, but I stick with this traditional version.
Note: do not use margarine, it will not work.