Start by preheating your oven to 350 degrees Fahrenheit. Line two large baking sheets with parchment paper or silicone baking mats so the cookies do not stick and brown evenly on the bottom.
In a medium-sized bowl, whisk together the all-purpose flour, baking powder, ground cinnamon, and ground nutmeg. Mixing these ahead of time ensures the spices and leavening agent are distributed perfectly throughout the dough.
In a large mixing bowl, beat the softened butter and granulated sugar together until the mixture is light and fluffy. This usually takes about two to three minutes with an electric mixer and is key to achieving that soft texture.
Add the egg, the half cup of eggnog, and the alcohol-free vanilla extract to the butter mixture. Beat on medium speed until everything is well combined, scraping down the sides of the bowl as needed.
Gradually add the dry ingredients to the wet ingredients. Mix on low speed just until the flour disappears. Be careful not to overmix the dough, as this can make the cookies tough instead of tender.
Drop rounded tablespoons of dough onto the prepared baking sheets, spacing them about two inches apart. Bake for 10 to 12 minutes, or until the edges are just lightly golden. The centers might look slightly soft, but they will firm up as they cool.
Let the cookies cool on the baking sheet for five minutes before transferring them to a wire rack. While they cool, whisk together the powdered sugar, three tablespoons of eggnog, and a pinch of nutmeg to create a smooth glaze. Once the cookies are completely cool, spread the frosting on top and sprinkle with a little extra nutmeg.
