Preheat the oven to 375*F. Prepare fruit: slice large fruit (like apples and strawberries) and keep small fruit (like blueberries) intact. Toss fruit with 1/4 cup flour and 3/8 cup sugar, and pour into a deep baking dish (roughly 9" x 13" x 2").
For the topping: mix 1 cup flour and 1/2 cup sugar together in a food processor. Add the butter pieces, and pulse until crumbly; the biggest clumps should be 2-3 inches. Turn off the processor and break the largest clumps with your hands, so that the pieces range from 1/4-inch to 1-inch in size. (If you don't have a food processor, you can use a fork instead.).
Pour the crumbles over the fruit, and bake the crisp. If using berries/soft fruit: pour crumbles over the fruit and bake 30-40 minutes, uncovered. If using apples/firm fruit: bake 20 minutes covered with foil (or until fruit starts softening), then pour crumbles over top and cook for 30-40 minutes uncovered.
When done, fruit should be cooked and crumbles browned. Cool for about 15 minutes, and serve warm. Crisp stores well, covered in the fridge, for up to 5 days.