Preheat the oven to 350F. Line 2 large baking trays with parchment paper.

Mix together the butter, 3/4 cup sugar, egg yolk, eggnog, and vanilla in a large bowl.

Add the flour, baking powder, and nutmeg and stir to combine.

Use a 1 1/2-tablespoon scoop to measure out the cookie dough. Roll the dough balls in the remaining 1/4 cup sugar to coat. Arrange the sugared dough balls on the prepared baking sheets.

Bake until the cookies are set along the outside and just a touch doughy in the center, about 15 minutes, rotating the trays once halfway through.

Cool the cookies on the trays and then remove.

For the frosting, mix together powdered sugar, butter and vanilla.  Add 1 Tbsp of eggnog at a time, until it reaches your preferred texture. 

Spread a small amount of frosting on each cookie and sprinkle with nutmeg.

Serve and ENJOY!