Preheat the oven to 350 degrees F (175 degrees C).
Toss apples with white sugar and 1/2 teaspoon cinnamon in a medium bowl to coat; pour into a 9-inch square baking dish.
Mix brown sugar, oats, flour, and 1 teaspoon cinnamon in a separate bowl. Cut in cold butter with 2 knives or a pastry blender until the mixture resembles coarse crumbs; spread over apples and pat down gently until even.
Bake in the preheated oven until golden brown and sides are bubbling, about 40 minutes.