Homemade Apple Crumble

This recipe builds upon your original, providing more detailed instructions
and suggestions for variations.
Ingredients:
For the Apple Filling:
5 large apples (Granny Smith, Honeycrisp, or a mix), peeled, cored, and sliced to about 1/4 inch thickness. Mixing apple varieties adds complexity to the flavor.
1/4 cup granulated sugar (adjust to taste depending on the sweetness of your apples)
1/4 cup packed light brown sugar (adds a caramel note)
1 teaspoon ground cinnamon
1/2 teaspoon ground nutmeg
1 teaspoon fresh lemon juice (brightens the flavor and prevents browning)
1 teaspoon vanilla extract (enhances the overall flavor)
1 tablespoon all-purpose flour or cornstarch (helps to thicken the juices)
Optional: 1/4 cup chopped walnuts or pecans (for added texture and flavor)
For the Crumble Topping:
1 cup all-purpose flour
1/2 cup old-fashioned rolled oats (provides a chewy texture)
1/2 cup packed light brown sugar
1/2 teaspoon ground cinnamon
1/2 cup (1 stick) unsalted butter, melted (can also use cold butter cut into small cubes for a more crumbly texture – see instructions)
Pinch of salt (enhances the sweetness)
Instructions: