BISCUIT TOPPING: In a food processor fitted with a steel blade or in a large bowl, stir together the flour, sugar, baking powder, and salt. Pulsing, or using a pastry blender in the bowl, cut in the butter until the mixture resembles coarse crumbs. Slowly add milk, pulsing, or stirring, until just combined. Turn out onto a floured counter or board and knead several times until the dough is holding together and pretty smooth. Pat out or roll into a square to fit the baking pan or dish. Place the dough on top of the fruit in the pan, pressing down at edges a bit.