Crumb Topping Using your hands, mix equal parts brown sugar and flour with half as much unsalted butter (e.g. 1/2 C brown sugar, 1/2 C flour, 1/4 C butter). It should stick together and form crumbs. Spread the mixture onto a baking sheet lined with parchment paper. Bake at 350 F for 20 minutes. Crumble any pieces that stuck together and put the crumbs on everything in sight!