Preparing the Filling:

1. Preheat Your Oven: Start by preheating your oven to 350°F (175°C).
2. Prepare the Apples: Peel, core, and slice the apples into thin, even slices. Place them in a large mixing bowl.
3. Add Lemon Juice: Drizzle the lemon juice over the apple slices to prevent browning and add a subtle tang.
4. Mix the Dry Ingredients: In a small bowl, combine the granulated sugar, ground cinnamon, nutmeg, and flour. Stir until well mixed.
5. Combine with Apples: Sprinkle the dry mixture over the apple slices and toss until the apples are thoroughly coated.
6. Transfer to Baking Dish: Pour the apple mixture into a greased 9×9-inch baking dish, spreading it evenly.

Preparing the Crumble Topping:

1. Mix Dry Ingredients: In a medium mixing bowl, combine the flour, rolled oats, brown sugar, cinnamon, and salt.
2. Cut in the Butter: Add the cold, cubed butter to the dry ingredients. Use a pastry cutter or your fingers to mix until the mixture resembles coarse crumbs.
3. Top the Apples: Evenly distribute the crumble topping over the prepared apple filling.

Baking:

1. Bake the Crumble: Place the baking dish in the preheated oven and bake for 40-45 minutes, or until the top is golden brown and the apples are tender.
2. Cool Slightly: Once baked, remove the dish from the oven and allow it to cool for about 10 minutes before serving.