Preheat the oven to 375°F (191°C). Lightly grease a 9- or 10-inch square baking pan, a deep-dish 9-inch pie dish, 10-inch cast iron skillet, or any 2–2.5-quart baking dish. Set aside.

In a medium bowl, whisk together the flour, brown sugar, baking powder, cinnamon, and salt. Add the melted butter and mix with a fork until the topping is completely moistened and clumps together. Do not overmix; you want it to be crumbly. Place the topping in the freezer while you continue.

In a large bowl, gently stir together all of the filling ingredients. Spread the filling evenly in the prepared baking pan.

Sprinkle the cold crumble topping evenly over the filling.

Bake for 40–50 minutes or until the topping is golden brown and the fruit juices are bubbling around the edges. Around the 30-minute mark, loosely cover with aluminum foil, to prevent the topping from over-browning. Remove from the oven, place on a cooling rack, and allow to cool for at least 20 minutes. The filling will continue to set as it cools. Serve warm with vanilla ice cream, if desired.

Cover leftovers and store in the refrigerator for up to 4 days.