In small bowl, mix egg whites and 1/4 cup buttermilk. Set aside.
In mixing bowl, beat butter and sugar until creamy, about 2-3 minutes. Add in dry ingredients and mix until combined. Slowly add in egg white mixture. Beat in remaining buttermilk.
Bake in a 350 degree oven for 18-20 minutes. Remove and cool completely before frosting.
For the frosting:
Beat butter for 3 minutes until fluffy. Add in nutmeg, rum flavoring, powdered sugar and eggnog. Beat for an additional 3-5 minutes until fluffy.
Pipe onto cupcakes using your favorite decorator tip. Add a sprinkle of nutmeg if desired! ENJOY.
Notes
Are rum flavoring and rum extract the same? They are not the same technically; rum flavor is made from artificial ingredients to imitate the flavor of rum. Rum extract is a highly concentrated liquid made from real rum. You can use either one in this eggnog frosting. Do not use real rum as it doesn't have enough concentrated flavor.
Can I use a boxed spice cake mix instead? Yes, boxed spice cake makes a fine swap if you don't want to make the cupcakes from scratch.
Store these Christmas cupcakes at room temperature in an airtight container. Enjoy within 4-5 days for best taste.
Can I freeze these cupcakes? These cupcakes are freezer friendly and will stay good in the freezer for 2 to 3 months. You can freeze them before or after adding the frosting.