Add 3 cups of milk and the half and half (or heavy cream) to the slow cooker. Turn on high.
In a blender add the remaining 3 cups milk, 40 Andes Mints, unsweetened cocoa powder and sugar and blended on high until mints are chopped up and unsweetened cocoa powder is mixed in, about 15-20 seconds. Pour into slow cooker and stir to combine.
Place lid on slow cooker and cook for 3-4 hours.
Making sure to stir every hour (or 45-minutes) to make sure that the cocoa is not burning to the bottom.
Serve with marshmallows, whipped topping, chopped up Andes Mints and chocolate drizzle.