Before You Begin:
Prepare your slow cooker and ingredients as needed. Cooking times and results may vary depending on your equipment and ingredients.
Prepare the apples
Peel, core, and slice the apples. Place them in a large bowl and toss evenly with granulated sugar, ground cinnamon, and any optional additions if using.
Layer the slow cooker
Lightly grease a 4–6 quart slow cooker. Spread the apple mixture evenly across the bottom of the slow cooker.
Make the topping
In a separate bowl, combine rolled oats, flour, brown sugar, and melted butter. Mix until a crumbly texture forms. Stir in chopped nuts if desired.
Assemble and cook
Sprinkle the topping evenly over the apples without pressing it down. Cover and cook on LOW for approximately 4–6 hours, or until the apples are tender when pierced with a fork. Cooking times may vary depending on slow cooker model and apple thickness.
Finish and serve
Once cooked, carefully remove the lid. For a slightly drier topping, allow steam to escape during the final portion of cooking if needed. Spoon into bowls and serve warm with optional toppings such as vanilla ice cream or whipped cream.