Preheat oven to 375°F (190°C). Line an 8x8 inch baking pan with parchment paper, leaving an overhang on two sides.
In a large bowl, combine flour, oats, and brown sugar. Cut in cold butter using a pastry blender or your fingers until mixture resembles coarse crumbs. Set aside 1 cup of the mixture for the topping.
Press the remaining crumb mixture into the prepared baking pan to form the base.
In a separate bowl, combine diced apples, granulated sugar, flour, cinnamon, and nutmeg. Toss to coat.
Pour the apple mixture over the crumb base. Sprinkle the reserved crumb topping evenly over the apples.
Bake for 35-40 minutes, or until the topping is golden brown and the apples are tender.
Let cool completely in the pan before lifting out using the parchment paper overhang. Drizzle with caramel sauce before slicing and serving.
Notes
Enjoy these bars warm or at room temperature. Store leftovers in an airtight container at room temperature.