Wash, peel, core, and slice the apples into small pieces.
In a large pot or slow cooker, combine the apple slices, granulated sugar, light brown sugar, cinnamon, cloves, allspice, nutmeg, salt, and apple cider or apple juice. Mix well to ensure that the apples are evenly coated with the sugar and spices.
If using a pot on the stovetop, cook the mixture over low heat, stirring occasionally, for about 6-8 hours. If using a slow cooker, cook the mixture on low heat for 10-12 hours or on high heat for 5-6 hours. The apples should become very soft and dark brown in color.
Once the apples are cooked and have reached the desired consistency, use an immersion blender or a regular blender to puree the mixture until smooth. Be cautious when blending hot liquids and allow the mixture to cool slightly if needed.
If the apple butter is too thin, return it to the pot or slow cooker and cook for an additional 1-2 hours, or until it reaches your preferred thickness.
Allow the apple butter to cool, then transfer it to sterilized jars, leaving about 1/4-inch of headspace. Seal the jars tightly with lids.
Store the apple butter in the refrigerator for up to 3 weeks or freeze it for longer storage. You can also process the jars in a boiling water bath canner for 10 minutes to make them shelf stable.