Instructions

1. Add the quartered apples, apple cider vinegar, apple cider, and lemon juice to a large saucepan and set it over medium-high heat. Bring the mixture to a boil, stirring frequently. Cover the pan, turn the heat to medium-low, and simmer for 20 minutes, stirring occasionally. The apple should be "crisp-tender"; if you poke a fork into one of the slices, it should slide in but with some resistance. If the apples have not reached this point, allow them to cook a bit longer. Remove the pan from the heat, keep covered, and let sit at room temperature for 6-8 hours.
2. Set a food mill that's fitted with the largest straining plate over the bowl of your slow cooker. Push the apples and all the liquid in the saucepan through the food mill into the slow cooker bowl, which will separate the apples from the core and peel. Add all the remaining ingredients, except the vanilla, to the apple pulp and stir to mix.
3. Cook the mixture on high for 8 hours, stirring every once in a while. Remove the lid and cook for an additional 3-4 hours on high, until the apple butter is thick and deep brown. (*See notes about temperature below.) To test that it's done, place a small dish in the freezer for a few minutes. Spoon a bit of the apple butter onto the frozen dish and let sit for about 5 minutes. This will cool the apple butter quickly, allowing you to test it's thickness.
4. Stir in the vanilla.
5. Store apple butter in the refrigerator for up to 1 month, in the freezer for up to 6 months.

To preserve apple butter, spoon into sterilized jars and process in a hot water bath for 10 minutes. 

1. Pour the hot mixture into very clean, dry glass jars leaving about 1/4 inch at the top. Using a damp cloth or paper towel, wipe the tops of the jar to ensure a clean seal. Cap and screw on lids, leaving them a bit loose.
2. Bring a large pot of water, or water-bath canner, to a rolling boil and gently lower the jars into the boiling water using tongs. The water should cover the jars by at least 1/2 inch. Let process for 10 minutes. Remove the jars from the water bath and place upside down on a dry towel laid out on a flat surface. Allow to cool completely.
3. Once the jars are cool, check the seal by gently pressing down on the center of the lid. If it pops up and down (often making a popping sound), it is not sealed. If that should happen to a jar or two, just store the preserves in the refrigerator and use it within 3 weeks. Properly sealed jars can be stored in the cupboard for up to 12 months.