01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish with butter or cooking spray.
02 - Spread lemon pie filling evenly across the bottom of the prepared dish. Distribute mandarin orange segments over the filling and sprinkle with fresh lemon zest.
03 - Sprinkle dry yellow cake mix evenly over the fruit layer. Do not stir or mix—layering creates the signature dump cake texture.
04 - Drizzle melted butter and whole milk over the cake mix, aiming to cover as much dry mix as possible. Sprinkle granulated sugar across the surface for added sweetness and caramelization.
05 - Bake for 35–40 minutes until the top turns golden brown and edges bubble vigorously. The cake should be set with slightly crisp edges.
06 - Cool for at least 15 minutes before serving to allow layers to set. Serve warm with whipped cream or vanilla ice cream. Refrigerate leftovers for up to 3 days.