Preheat oven to 350 degrees.

In a medium mixing bowl, whisk together flour, baking powder, nutmeg, cinnamon, allspice/clove, and salt. Set aside.

Cream butter using a stand mixer or electric handheld mixer on medium speed, about 2 minutes. Add white and brown sugar and continue to cream until light and fluffy. Beat in egg yolks one at a time until blended. Add eggnog and mix until combined.

With the mixer on low, gradually stir in dry ingredients until just combined. For thicker cookies, let dough chill for 30 minutes in frig.

Once dough is chilled, preheat oven to 350 degrees F.

Form dough balls with about 2 tablespoons of batter. Roll in granulated sugar to coat (optional). Arrange on cookie sheet with about 2 inches between each cookie. Bake until edges of cookies are just set, middle will still be a little undercooked, about 10-12 minutes. Let rest on cookie sheet for 5 minutes, then cool completely on a wire rack.

Once cookies are cool, prepare the frosting. Beat softened butter on medium speed with a stand mixer or electric mixer until smooth and creamy, about 3 minutes. Add powdered sugar, eggnog/milk, nutmeg, and a pinch of salt and beat on high until frosting is fluffy, about 1-3 minutes, scraping down sides when necessary. Add more eggnog if frosting is too thick and add more powdered sugar if frosting is too runny.

Frost cookies, either by piping on with a frosting bag or spreading on with a knife. Sprinkle with extra nutmeg and sprinkles, and serve!