Core the apples and then slice them into quarters. Leave the skin on. Place the apple quarters into the crock pot. Fill to the top.
Turn the slow cooker on high heat and cook for 4 hours.
After 4 hours, using an immersion blender, blend all the apples into a sauce. If you don’t have an immersion blender, you can use a regular blender but will have to do it in multiple batches.
Add the cinnamon and stir to combine. Store in an airtight container in the fridge.