Whisk six 12-ounce cans evaporated milk, 1/3 cup chocolate liqueur and 1/4 cup peppermint schnapps in a slow cooker. Add two 12-ounce bags dark chocolate chips. Cover and cook on low for 2 to 3 hours, stirring occasionally. Ladle into mugs. Garnish with whipped topping and candy canes.
If you don't have a slow cooker, keep these drinks warm in a saucepan on the stovetop over low heat.