This eggnog frosting tastes just like the holiday drink. It's not surprising because the eggnog frosting is made with rum, nutmeg, and - keeping true to traditional eggnog - egg yolks.
Follow Brave Tart's Faux French Buttercream instructions using all ingredients except the nutmeg and rum. Brave Tart explains how to make French buttercream so well that I dare not even try to repeat her directions here. However, if you prefer cups to weights, you can use my measurements above instead of hers. My ingredient list is also considerably scaled down; hers makes enough to frost a three layer cake and mine frosts 10 cupcakes.