Cook the apple peels and cores: Place the peels and cores from 3 lbs of apples in the crockpot. Add 1 cup of apple juice to the crockpot to prevent burning. Set the crockpot to low heat and cook for 2 hours, allowing the apples to soften and release their juices.
Strain the apple mixture: Turn off the crockpot and spoon about a quarter of the cooked scraps or apples into a fine mesh sieve or a tomato mill. Position the sieve over a medium-sized mixing bowl. Using the back of a metal spoon, press the apple mixture against the sieve, forcing the soft apple scraps through. Scrape down the outside of the sieve with the spoon to gather as much of the cooked apple puree as possible. Repeat this process until you’ve strained all the apple mixture.
Combine all ingredients in the crockpot: Return the cooked apple puree to the crockpot. Add the remaining apple juice, brown sugar, granulated sugar, cinnamon, cloves, and nutmeg. Stir to evenly distribute the spices and sugars throughout the mixture.
Set the crockpot to low heat: Cover the crockpot with the lid and cook on low heat for 4-5 hours. During this time, the apple puree will break down further, and the flavors will meld together.
Stir occasionally: Every few hours, give the mixture a gentle stir to ensure even cooking and to prevent sticking.
Blend the mixture: After 8-10 hours, once the apple puree is completely soft and the mixture is thickened, use a blender or an immersion blender to puree the apple butter until smooth. If you prefer a chunkier texture, you can blend it less.
Cook uncovered to thicken (optional): If the apple butter isn’t as thick as you’d like, continue cooking it in the crockpot with the lid off for an additional 1-2 hours, stirring occasionally until it reaches your desired consistency.
Cool and store: Once the apple butter has thickened to your liking, allow it to cool. Transfer it to clean jars or airtight containers. Store in the refrigerator for up to 2 weeks or water bath can for 25 minutes for longer storage.