½cup (1 stick or 113 g)butter, cubed and at room temperature
MAKE THE FRUIT FILLING
Preheat the oven to 375° F. Spray a baking dish (9 by 13 or anything that's at least 2 inches deep) with baking spray and set aside.
Place the fruit in a large bowl and add the tapioca starch, sugar, and lemon juice. Mix to combine. Dump the fruit mixture into the prepared pan and set aside.
MAKE THE CRUMBLE
Whisk together the flour, baking powder, brown sugar, and salt in a medium bowl. Add the cubed butter and, using a pastry cutter, a fork, or your fingers, work it into the dry ingredients until a dough forms.
Break up this dough into big and small pieces all over the top of the fruit. Place the pan on a larger baking sheet (to catch any drips) and bake the fruit crumble for 35-40 minutes, or until the crumble is golden brown and the fruit is bubbling (for the tapioca to properly thicken the fruit, it must be bubbling).
Remove from the oven and serve warm with vanilla ice cream, if desired.
For certain fruits, the baking time may be longer (such as apples or pears). Check for doneness by inserting a knife into the fruit. If it goes in with little to no resistance, it's done. If not, bake for 10 more minutes and check again. If the top is getting too dark, cover it loosely with foil.