Slice apples and heap them into a six quart slow cooker.
Add 1/2 cup water and set to low.
Cook until apples are tender and can be easily pressed into sauce. On low, this will take 4-6 hours. On high, it should only take 2-3 hours.
Puree softened apples into a smooth puree (it shouldn't be necessary to peel).
Return to puree to slow cooker and cook on low for 6 hours with the lid set slightly ajar so that it can vent.
Add 1/2 cup sugar, spices and lemon zest/juice. Taste and add more spices and sugar, if necessary.
Funnel hot apple butter into prepared jars, leaving 1/2 inch headspace.
Wipe rims, apply lids and rings and process in a boiling water bath canner for 15 minutes.
When the time is up, turn off the heat and remove the lid. Let the jars rest in the cooling water for 5 minutes. When that time has elapsed, remove the jars and set them on a folded kitchen towel to cool. When the jars have cooled enough that you can comfortably handle them, check the seals. Sealed jars can be stored at room temperature for up to a year. Any unsealed jars should be refrigerated and used promptly.