Core and slice apples (can leave on the skins) and add them to the basin of a slow cooker. Pour apple cider vinegar over the apples and cover with lid.
Cook for 8 hours on low, stirring occasionally. Ensure the apples are kept moist and don't burn. If mixture looks too dry, add ¼ cup of water for moisture. Can repeat this process as needed, but add sparingly, ideally only once or twice. Adding too much will extend the cooking time to get that nice thick apple butter texture at the end.
Once the apples are simmered and mushy, add them (skins and all) to a blender or processor and process until smooth.
Return the blended mixture to the slow cooker. If you want to add more sweetness, add ⅛ cup brown sugar. Add the spices and mix thoroughly. Taste as you go and adjust the flavorings to your preference.
Cook on high, uncovered until desired consistency is reached. I like my apple butter a little thinner so it usually takes 30-60 minutes.