For the filling:
- 3 pounds Granny Smith apples
- 1 cup white sugar
- 1 tablespoon all-purpose flour
- 2 teaspoons ground cinnamon
For the topping:
- 1 1/2 cups quick-cooking oats
- 1 1/2 cups all-purpose flour
- 1 1/2 cups packed brown sugar
- ½ teaspoon baking powder
- ¼ teaspoon baking soda
- 3/4 cup butter melted