Let's cook.
Preheat your oven to 375°F (190°C). Lightly grease an 8x8 inch baking dish.
In a large bowl, combine the sliced apples, granulated sugar, cinnamon, and nutmeg. Toss gently until the apples are evenly coated. Pour the apple mixture into the prepared baking dish.
In a separate medium bowl, combine the flour, rolled oats, and brown sugar. Mix well.
Add the cold, cubed butter to the dry ingredients. Use your fingertips or a pastry blender to cut the butter into the mixture until it resembles coarse crumbs.
Sprinkle the oat crumble topping evenly over the apple mixture in the baking dish.
Bake for 40 minutes, or until the apples are tender and the topping is golden brown and crisp. You can test the apples for tenderness by gently piercing them with a fork.
Remove from the oven and let cool for at least 10 minutes before serving. This allows the filling to set slightly.
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