Good with blueberries too (use one quart).
Preheat oven to 350°F. Grease a shallow baking dish.
Place apples in prepared baking dish.
In a saucepan over medium heat, melt butter. Stir in brown sugar, oats, flour, and cinnamon and mix well. Sprinkle mixture over the apples.
Bake for 45 minutes, or until top is golden and apples are soft.
Serve warm with whipped cream or vanilla ice cream.