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.

Cook in slow cooker on low for about 10 hours, stirring occasionally, until the mixture is thickened and dark brown.

Uncover, stir in vanilla and continue cooking uncovered on low for about 2 hours.

Use an immersion blender to puree the apple butter until smooth.

Fill a large stockpot or canning pot with water. It should be enough so that your filled jars will be covered by at least 1 inch. Cover and set to boil.

Set 4 pint jars or 8 half-pint jars, lids, and rings on a towel-lined countertop.

Using a pair of tongs, dunk the jars into the hot water and empty, then set on the towel again. This is to warm the jars to prevent cracking when the hot apple butter is added.

Ladle the hot apple butter into the jars, leaving ¼ inch of space at the top of the jars.

Use a chopstick or kitchen dowel to gently remove any trapped air bubbles.

Wipe rims of the jars clean with a damp paper towel.

Place the lids, then screw on the rings to fingertip tight - it should not be able to move freely, but can be easily unscrewed.

Using a jar lifter, carefully lower the jars into the boiling water bath.

Return the water to a boil, cover, and boil jars for 15 minutes for pint jars, or 10 minutes for half-pint jars.

Turn off the heat and let the jars sit for 5 minutes. Then use the jar lifter to carefully remove the jars and place on the towel-lined countertop.

Let the jars rest, undisturbed, for 24 hours. You might hear a pinging noise as the jars seal.

After the jars have rested, check for seals, label, and store in the pantry for up to 18 months.

Any unsealed or opened jars of apple butter must be stored in the refrigerator.