For the topping:
1 1/4 cups all-purpose flour
3/4 cup rolled oats
1/2 cup packed brown sugar
1 teaspoon ground cinnamon
1/4 teaspoon kosher salt
8 tablespoons unsalted butter, melted
For the filling:
Butter or cooking spray, for coating the slow cooker
6 medium apples (about 3 pounds), peeled, cored, and cut into 1-inch chunks
1/3 cup granulated sugar
2 tablespoons all-purpose flour
1 teaspoon ground cinnamon
1 tablespoon lemon juice
Place the flour, oats, sugar, cinnamon, and salt in a medium bowl and stir to combine. Pour in the melted butter and stir until the butter is completely incorporated into the dry ingredients and the mixture is wet and crumbly; set aside.
Generously coat the insert of a 6-quart or larger slow cooker with cooking spray or butter.
Add the apples, sugar, flour, cinnamon, and lemon juice to the slow cooker, stir to combine, and spread into an even layer. Sprinkle the oat topping evenly over the apples.
Place a large sheet of paper towels over the slow cooker, making sure it completely covers the top of the slow cooker, but does not sag down onto the crisp. Cover with the slow-cooker lid. Set the slow cooker to HIGH and cook for 1 1/2 hours, or cook on LOW for 2 1/2 to 3 hours.
Remove the lid and paper towels and cook, uncovered, until the topping is browned and crisp and the fruit is tender, about 1 more hour. Let the crisp cool at least 15 minutes uncovered before serving.
Recipe Notes
- Storage: Store the crisp in a covered container in the refrigerator for up to 5 days. Serve cold, room temperature, or rewarmed in a 300°F oven for 20 minutes.