Preheat your oven to 350°F. Spray the 9x9-inch baking dish with nonstick cooking spray.
FILLING
Peel, core, and thinly slice the apples.
In a large bowl, combine the sliced apples, granulated sugar, brown sugar, cinnamon, nutmeg, allspice, lemon juice, and cornstarch. Toss until the apples are evenly coated.
Spread the apple mixture in the bottom of the baking dish and spread into an even layer.
TOPPING
In a medium bowl, mix together the oats, flour, brown sugar, granulated sugar, cinnamon, and salt.
Add the cold butter cubes and use a pastry cutter or your fingers to work the butter into the mixture until it resembles coarse crumbs. Stir in chopped nuts, if desired.
Sprinkle the topping in an even layer over the apple mixture.
BAKE
Bake for 35-40 minutes or until the topping is golden brown and the apples are tender when poked with a fork.
Remove the apple crisp from the oven and let it cook for 5-10 minutes.
Scoop the apple crisp into bowls and top with a scoop of vanilla ice cream, if desired. Drizzle with caramel sauce, if desired.
Notes
Storage: Let the apple crisp cool to room temperature then cover with foil or transfer to an airtight container. Store in the fridge for up to 4 days.