If you're using frozen fruit, use them from frozen; no need to thaw.
For the fruit:
- 3 pounds (1.36 kilograms) fresh or frozen fruit (like berries, sliced peaches, sliced apples, sliced plums, etc.)
- 1/2 cup (100 grams) sugar, plus more to taste
- 2 1/2 tablespoons cornstarch
- 1/8 teaspoon kosher salt
For the cake:
- 1 cup (200 grams) sugar
- 1 1/4 cups (175 grams) all-purpose flour
- 1 teaspoon baking powder
- 1/4 teaspoon kosher salt
- 3/4 cup (170 grams) melted unsalted butter
- Vanilla ice cream, to serve
1 Preheat the oven to 375°F.
2 Prepare the fruit: Combine the fruit, sugar, cornstarch, and salt in a 9x13 baking dish, stirring to coat the fruit in the sugar and cornstarch. Add up to an extra 1/4 cup sugar, as needed, if using very tart fruits. (Frozen fruit is fine; it doesn't not need to be thawed before baking.)
Spread the mixture into an even layer.
3 Add the cake topping: Whisk together the flour, sugar, baking powder, and kosher salt for the cake layer in a mixing bowl. Sprinkle the mixture evenly over the top of the fruit. Drizzle the melted butter evenly over the top.
4 Bake the cake: Bake for 35 to 45 minutes, or until the fruit is bubbling through the center and the top is golden (frozen fruit might take an extra 10 minutes or so). If you notice a few dry pockets of flour toward the end of cooking, push them down into the fruit with a spoon so they cook.
Serve warm with vanilla ice cream. Leftover cake can be covered and refrigerated for a few days.