Preheat oven to 375°F.
Grease a 9in x 13in baking dish.
Peel and thickly slice apples and place in greased dish.
Combine the sugar, flour, and cinnamon in a mixing bowl.
Cut butter into ¼inch pieces, then cut into the dry ingredients to make crumbs. Use your fingers, a pastry blender, or food processor.
Distribute mixture over apples, but do not press down.
Bake for 45-60 minutes, until slightly brown and there is no resistance when apples are pierced with a knife.
Cool on rack at room temperature.