Add the peeled, cored and cut apples into a 6-quart slow cooker. Add the brown sugar (make sure to break up any hard clumps with your fingers). Add the cinnamon, nutmeg, cloves, and salt.Stir.Cover and cook on LOW for 10 hours.After the apples have cooked, place them and any liquid that the apples made into a blender, cover with lid, and a towel on top of that (to prevent burns, in case the lid flies off). Hold the lid on while the blender is on. Pulse for about a minute, until very smooth.At this point if your apple butter isn't as thick as desired, pour it back into the slow cooker. Turn the slow cooker back to LOW, and leave the lid off. Stir every 15 minutes. Mine took about 45 more minutes to thicken to perfection.Put into containers and refrigerate. I personally will store in the fridge for no longer than a week, or in the freezer for a few months.