Pour milk into the slow cooker and add in spices, sugar and vanilla. Stir to combine.
Cover and cook on low for 3 hours, but keep an eye out if it gets too hot because you don’t want the milk to boil.
After 3 hours turn off the slow cooker. Pour into mugs about half way and then add hot coffee to fill up the mugs. Stir to mix. Garnish with whipped cream if desired.