Preheat the oven to 350F degrees and line a 12 cavity muffin tin with cupcake papers. You may end up with a few more than 12 cupcakes - so you might need to line 2 trays.
In a medium sized bowl, whisk together the flour, nutmeg, baking soda & salt. Set aside.
In a large bowl using a stand or hand-held electric mixer, beat the butter and sugar together on medium speed until light and fluffy. Add in the egg whites & vanilla and continue mixing. Turn off the mixer and scrape down the sides of the bowl.
Slowly add the flour mixture and eggnog while mixing on low speed, alternating between adding half the flour mixture followed by half of the eggnog.
Pour about ¼ cup of batter into each cavity of the prepared muffin tin - each should be about ⅔ full. Bake for 14-16 minutes until an inserted toothpick comes out clean. Allow cupcakes to cool in their pan for 10 minutes, then transfer to a wire rack to continue cooling.
While the cupcakes are cooling, you can start making the icing. Beat the butter using a hand held or stand mixer on medium speed. Add in the salt & vanilla, and mix in the icing sugar about 1 cup at a time. After you've added about 2 cups of the icing sugar, add the whipping cream 1 tablespoon at a time. Alternate adding the last cups of icing sugar with whipping cream until the desired consistency is reached. Frost cupcakes using a piping bag or spreading the icing with a flat knife.