How to Make It
Whisk together 4 cups whole milk, 1 cup heavy cream, and 1/2 cup white buttermints in a medium saucepan. Bring to a simmer over medium, stirring constantly, until mints are dissolved and mixture is hot, about 13 minutes.
Remove from heat and whisk in 6 ounces chopped white chocolate and 2 teaspoons vanilla extract until smooth. Stir in 1/3 cup Irish cream liqueur (such as Baileys Irish Cream).
Pour into 4 serving cups, and top each with 1/4 cup marshmallows. Garnish with mint sprigs and crushed buttermints, if desired.