1. Preheat oven to 350Grease 2 9x13 sized pans with butter and dust with cocoa powder, set aside.Prepare cake according to package directions, but add in an extra egg to the mix.Split the batter evenly between the 2 pans and bake for 15-20 minutes until a toothpick comes out clean.Allow cakes to cool completely.In stand mixer beat butter and Fluff together until smooth.Turn mixer to low and slowly add in powdered sugar. Turning mixer back up, continue mixing for 30-60 seconds until smooth.
2. Spread the filling on top of one of the cakes. Top the filling with the other cake.In small saucepan bring the heavy cream to almost a boil.
3. Remove from heat and stir in chocolate chips. Allow to cool for 10 minutes and then pour over top of cake.