In a 4-quart slow cooker, add in the apples, brown sugar, peanut butter, and flour. Stir until the apples are coated and everything is incorporated
In a large bowl, add in the butter and peanut butter. Mix on medium until combined.
Add in the brown sugar, flour, and oats and mix on medium until a crumbly mixture forms. Sprinkle the topping on the apples. It's a thick topping, so set aside some if it's too much for your liking.
Cover slow cooker with a paper towel and set to low. Let cook for 2 hours 45 minutes to 3 hours 15 minutes. It depends on how you want your apples done. Mine were slightly firm, but not crunchy and I turned the heat off at 2 hours 45 minutes.
Scoop and serve. Add a scoop of ice cream too!