Rhubarb Dump Cake

Prepare the Fruit: Place the chopped rhubarb and berries in a greased 9×13-inch baking dish. Sprinkle the granulated sugar and dry gelatin powder evenly over the fruit.
Layer the Cake: Pour the dry cake mix directly over the fruit layer, spreading it out with a spatula to cover the edges.
Add Butter: Drizzle the melted butter slowly over the entire surface of the cake mix. Try to cover as much of the dry mix as possible to ensure a crisp crust.
Bake: Place in a preheated oven at 350°F (175°C) for 40–50 minutes. The cake is done when the fruit filling is bubbling up at the sides and the top is a deep golden brown.
Cool and Finish: Let the cake rest for at least 15 minutes to allow the fruit filling to thicken. Dust the top generously with powdered sugar before serving.

Rhubarb Custard Style: Whisk 2 eggs into the melted butter before drizzling it over the cake mix for a richer, more custard-like topping.
Crunchy Nut: Add 1/2 cup of chopped walnuts or pecans to the cake mix layer for added texture.
Ginger Spice: Mix 1 teaspoon of ground ginger into the rhubarb for a warm, spicy contrast to the tart fruit.

Service: This cake is best served warm, ideally with a scoop of vanilla ice cream to balance the tart rhubarb.
Storage: Cover and store at room temperature for up to 2 days, or in the refrigerator for up to 5 days.
Reheating: Reheat individual portions in the microwave for 20 seconds or in a low oven to restore the crispness of the topping.