1. Place the apples in a slow cooker. In a medium bowl, combine sugars, cinnamon, nutmeg cloves and salt. Pour the mixture over the apples and mix well.
2. Cook in slow cooker on low for about 10 hours, stirring occasionally, until the mixture is thickened and dark brown.
3. Uncover, stir in vanilla and continue cooking uncovered on low for about 2 hours.
4. Use an immersion blender to puree the apple butter until smooth.
5. Spoon the mixture into sterile containers, cover and refrigerate for up to two weeks or freeze.
6. Serve on breads, muffins, pork chops or just eat it with a spoon.