1 1/2 cups milk
1/2 cup eggnog
1 (1 ounce) square semi-sweet chocolate
3/4 cup mint-chocolate baking pieces (such as Andes®)
Heat milk and eggnog together in a saucepan over medium-low heat until heated through, about 5 minutes. Stir in chocolate and mint-chocolate baking pieces; cook until chocolate is melted and smooth, 5 to 10 more minutes. Pour into 2 mugs.