Instructions. Pour the dry cake mix over the pie filling, spreading it evenly. Pour the stick of melted butter over the cake mix. How to Make Lemon Dump Cake. Spray a 9×13-inch baking dish with nonstick cooking spray. Preheat the oven to 325ºF. Spread the pie filling in the bottom of the baking dish. Preheat oven to 400. Pour the 2 can of lemon pie filling in the bottom of a 9*13 cake pan or baking dish that has been greased with cooking spray.