Preheat your oven to 375°F (190°C). Gather your peeled, sliced apples and place them in a large mixing bowl.
Toss the apple slices with granulated sugar and cinnamon until evenly coated. Spread them out in the bottom of a greased baking dish.
Tear the biscuit dough into rough chunks and layer them over the apples, distributing evenly across the dish.
Mix the melted butter with vanilla extract and milk in a small bowl, then pour it evenly over the biscuit pieces and apples. Ensure the mixture soaks into the layers for a tender bake.
Sprinkle the brown sugar and a little cinnamon over the top for a caramelized crust. Place the dish in the oven and bake for about 35 minutes, or until bubbling and golden around the edges.
Remove the casserole from the oven once the top is crisp and golden, and the apples are tender. Allow it to cool slightly before serving, to let the flavors meld and the topping set.