Slice apples (peeling optional) and place in the bowl of your Crock-Pot slow cooker. Add brown sugar, cinnamon, ginger, nutmeg, cloves, lemon juice, and apple cider. Toss together until the apples are evenly coated.

Cover and cook on LOW for 10 hours, until apples have completely broken down and the mixture is deep in color and fragrant.

Carefully transfer the apple mixture to a blender, working in batches if needed, and pulse until completely smooth. Let the mixture cool slightly before blending and hold a towel over the lid. Pour the blended apple butter back into the slow cooker.

In a small bowl, whisk together the corn starch and vanilla extract to form a smooth slurry. Pour into the apple butter and stir well to combine.

Cook uncovered on HIGH for 30 minutes to 1 hour, stirring occasionally, until the apple butter reaches your desired thickness. Test by placing a spoonful on a cold plate. It should hold its shape without releasing a ring of liquid around the edges.

Let cool completely, then transfer to mason jars or airtight containers. Refrigerate for up to 3 weeks or freeze for up to 1 year.