Place the baking dish on the middle rack of the preheated oven. Bake for 35–45 minutes, or until the top is golden brown and crisp and the fruit is bubbling up around the edges and in a few spots in the middle. If your oven runs cool, it may need a few extra minutes.
Remove the dump cake from the oven and let it cool for at least 10–15 minutes so the fruit layer can thicken slightly. The top should look crisp and golden with bits of bubbling fruit peeking through.
Serve warm, scooped straight from the glass dish into bowls. Add ice cream, whipped cream, or yogurt if you like. Store any leftovers covered in the fridge for up to 3 days; reheat portions in the microwave or a low oven until warmed through.
To keep this as low-fuss as Aunt Denise would, stick to the three-ingredient base and just tweak flavors. For extra texture, you can sprinkle 1/2 to 3/4 cup chopped nuts (like sliced almonds or chopped pecans) over the cake mix before drizzling on the butter. If you like things a little tart, add a squeeze of fresh lemon juice or a tablespoon of lemon zest to the pie filling before spreading it in the dish. For a slightly spiced version, dust 1/2 to 1 teaspoon ground cinnamon over the dry cake mix. If you can’t find strawberry rhubarb pie filling, you can use 1 can strawberry pie filling and 1 can rhubarb pie filling, or mix strawberry and cherry. To make individual servings, divide the ingredients among smaller oven-safe dishes or ramekins and reduce the bake time slightly, watching for that same golden, bubbly look. If you prefer a less rich top, use the 1/2 cup butter as written; if you want that extra buttery, almost cobbler-like crust, go up to 1 cup melted butter. This dessert is very forgiving, so use what you have on hand and don’t stress about perfection—just bake until the top is golden and the fruit is bubbling.
