Spray insides of slow cooker with cooking spray for easy cleanup and set aside.
Peel, core, and chop the apples.
Place ½ of the apples and 1/2 cup of cider into a high power blender and secure lid.
Blend for 10-15 seconds, if necessary, use the tamper to press the ingredients into the blades. Increase speed and blend for 1 to 2 minutes until the mixture is smooth. Transfer the mixture to the slow cooker.
Repeat with the remaining apples and cider. Add apple mixture to the crockpot.
Stir in sugar and spices.
Cover and cook for 4 hours on high or 8-10 hours on low, until the mixture is dark brown. Taste and adjust for sugar. Freeze or add the apple butter to mason jars and store in the fridge for 2 weeks.