Pre-heat oven to 350 degrees. Line a 12-cup cupcake pan with liners and set aside.
In a large bowl, combine your dry ingredients, spices and whisk to combine, then set aside.
In the bowl of a stand mixer fitted with a paddle attachment, cream the butter until smooth about 2 minutes. Slowly add in the sugar and continue to beat for another 3 to 5 minutes until light and fluffy.
Add the mascarpone and beat until combined. Beat the egg whites until slightly foamy. Add to the butter sugar mixture in three pours. Beat after each addition until incorporated. Add the vanilla extract and Bourbon.
Add ½ of the dry ingredients and mix until just incorporated. Add the eggnog and combine. It will curdle some, that’s ok. Last, add the rest of the dry ingredients and mix to combine. Do not over mix.
Using an ice-cream scoop or about ⅓ cup, fill each cupcake liner ¾ full. Gently even out tops with offset spatula or knife.
Bake on middle rack of the oven for 16 to 18 minutes until toothpick inserted comes out clean.
Let cool for 10 minutes in pan on rack. Then remove from pan and allow to cool completely on the rack.
For the buttercream:
Place egg whites, salt and sugar in the bowl of a stand mixer. Place bowl over medium saucepan with about an inch of simmering water on the stove top.
Whisk constantly until the sugar is dissolved. Should take about 10 minutes. You can tell when it’s done by rubbing a small amount of the mixture between your fingers. If there is no graininess, it’s done.
Remove bowl from double boiler and attach to the stand mixer fitted with the whisk attachment. Whisk on medium high until stiff peaks form, about 10 minutes and the bottom of the bowl is cool to the touch.
Switch to the paddle attachment and your butter slowly a piece at time. Mixture will eventually curdle but keep mixing until smooth and shiny. Add the vanilla extract, Bourbon and eggnog, starting with ¼ cup of nog. Mix to combine. Taste and if desired add more eggnog a tablespoon at time until your desired nog flavor is achieved.
Frost cooled cupcakes as desired. Sprinkle top with ground nutmeg.Store covered in the fridge for up to 5 days. Allow to come to room temperature before serving.
Recipe by Social Buttercream at http://socialbuttercream.com/2018/11/17/pumpkin-spice-eggnog-cupcakes-have-your-cake-and-eat-it-too-along-with-pie/