Add the flavor of the Christmas eggnog into your frosting. Made with homemade eggnog, this eggnog buttercream is simple, easy, and delicious. With a touch of spices like nutmeg and cinnamon infused with a little booze, this custardy drink is the perfect festive treat. It takes five minutes to make and can be used to frost it over cakes, cupcakes, or between macaron shells.