For an extra layer of flavor, try using a high-quality, homemade eggnog. Adjust the amount of peppermint extract to your preference. Start with 1/4 teaspoon and add more to taste. If you want a thicker milkshake, freeze the eggnog in ice cube trays before blending. To make this a boozy treat, add a shot of rum or bourbon to the blender. Feel free to experiment with other toppings, such as chocolate shavings or a drizzle of caramel sauce. For visual appeal, try rimming the glass with crushed peppermint before pouring in the milkshake. For best results, use high-quality vanilla ice cream. The better the ice cream, the better the milkshake!