1. In a large mixing bowl, beat together 0.5 cup unsalted butter and 0.5 cup granulated sugar until light and fluffy, about 2-3 minutes.

2. Mix in 1 egg yolk, 0.5 teaspoon vanilla extract, and 0.25 cup eggnog until fully combined.

3. In a separate bowl, whisk together 1.5 cups all-purpose flour, 0.5 teaspoon baking powder, 0.25 teaspoon salt, and 0.25 teaspoon ground nutmeg.

4. Gradually stir the dry ingredients into the wet mixture until a soft dough forms. Do not overmix.

5. Cover the dough and refrigerate for 30 minutes to chill.

6. Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper. Roll dough into 1-tablespoon balls, spacing them 2 inches apart.

7. Bake for 10-12 minutes or until edges are set and centers look puffy.

8. Cool on sheet for 5 minutes, then transfer to a wire rack.

9. For the glaze, whisk 1 cup powdered sugar with 2 tablespoons eggnog until smooth.

10. Drizzle glaze over cooled cookies and sprinkle lightly with extra nutmeg.