Make Cupcakes

1. Preheat oven to 350º
2. Cream butter and sugar until light and fluffy
3. Add egg yolks and vanilla
4. Sift together dry ingredients and with a stand mixer on medium speed, alternate adding dry ingredients and sour cream, beginning and ending with the dry ingredients. Set aside
5. Whip the egg whites and sugar until stiff and gently fold into the batter in 3 additions
6. Line cupcake tins with paper liners. Fill each liner ¾ of the way full with batter
7. Bake for 10-11 minutes. Rotate the pan halfway through the cooking time for cupcakes to bake evenly
8. Allow to cool completely, then pop them in the freezer for at least 1 hour

Make Frosting

1. Cream room-temperature butter and powdered sugar (1 cup at a time - assure that mixer is on low speed when adding powdered sugar!), until 4 cups are added
2. Add vanilla bean paste or extract. Taste and adjust sweetness to your liking. Add 5th cup of powdered sugar if desired. If adding color, beat in drops of food coloring slowly until desired hue is achieved
3. Transfer to a piping bag and decorate cupcakes as desired, then assemble your tree!