• Preheat the oven to 375°F. Spray or grease a 9- or 10-inch deep-dish pie plate or baking dish.

Bumbleberry Filling

• In a large bowl, combine the apples, rhubarb, strawberries, blueberries and raspberries. Add the lime juice and toss to coat. In a small bowl, combine the sugar, arrowroot, mint, and half of the lime zest. Add the lime zest mixture to the fruit and toss well. Let sit, uncovered, for 10 minutes to release the juices.

Crumble Topping

• Meanwhile, in a medium bowl, whisk together both flours, the baking powder, both sugars and the remaining lime zest. Grate the butter into the bowl on the large side of a box grater. Rub the mixture together with your fingertips until it has a sandy texture with some larger pea-sized lumps.

Assembly

• Transfer the filling to the prepared pie plate. Sprinkle the crumble topping over top, making sure there are lumpy bits throughout. This gives it texture and a shortbready feel.
• Place the pie plate on a baking sheet. Bake for 30 minutes. If the topping is getting too browned at this point, cover loosely with foil. Continue baking until the juices are bubbling throughout and the topping is golden brown, 20 to 30 minutes. Remove the baking sheet and transfer the pie plate to a cooling rack. Let rest until the juices settle and thicken slightly, about 30 minutes.
• Serve with generous amounts of vanilla ice cream.