PREHEAT oven to 350 degrees F. Line a muffin tin with 12 paper liners.
WHISK together the flour, baking powder, baking soda, salt, and nutmeg. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, BEAT the butter on medium-high speed until creamy, scraping down the sides. ADD the sugar and beat until creamy and light in color, again scraping down the sides as needed.
ADD the vanilla and the eggs one at a time. MIX until the batter is smooth.
ADD about a quarter of the flour mixture to the wet ingredients and mix on low until combined. MIX in a few tablespoons of the eggnog. CONTINUE ADDING the flour mixture and the eggnog alternately, ending with the flour mixture. The batter will be thick.
DIVIDE evenly between 12 paper muffin liners, filling close to the top.
BAKE at 350 degrees F for 20-25 minutes until a toothpick or cake tester inserted in the center comes out clean.