1. Preheat oven to 350°F (175°C). Lightly butter a 9×13-inch baking dish.

2. Peel, core, and slice apples into ¼-inch thick pieces. Place in a large bowl.

3. Toss apples immediately with lemon juice to prevent browning.

4. Add granulated sugar, 2 tablespoons flour, cinnamon, nutmeg, ginger, and vanilla extract to apples. Stir gently until evenly coated.

5. Spread apple mixture evenly in the prepared baking dish.

6. In a separate large bowl, combine oats, 1 cup flour, brown sugar, cinnamon, and salt.

7. Add cold butter cubes to the oat mixture. Use a pastry blender or two forks to work butter into dry ingredients until mixture resembles coarse crumbs with pea-sized butter pieces.

8. Stir in chopped nuts if using.

9. Sprinkle crisp topping evenly over apples, covering completely. Do not press down.

10. Bake for 45-50 minutes, until topping is golden brown and filling is bubbling around edges.

11. If topping browns too quickly, tent loosely with aluminum foil.

12. Remove from oven and let cool for 15-20 minutes before serving.

13. Serve warm with vanilla ice cream or whipped cream.