Step 1

Preheat oven to 375°F. Butter a shallow 12-inch cast-iron skillet. Toss together apples, blackberries, sugar, cornstarch, lemon zest and juice, and salt in a bowl. Transfer to prepared skillet. Scatter topping over fruit.

Step 2

Bake until topping is browned and fruit is bubbling, 50 minutes to 1 hour (cover with foil after 20 minutes if crumble becomes too dark before fruit is bubbling). Let cool on a wire rack 10 minutes before serving. Serve with Sour Cream Whip alongside.