• Preheat your oven to 350 then line an 8x8 inch square baking pan with parchment paper, leaving some overhang for easy removal.
• In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy, which should take about 2-3 minutes.
  1/2 cup butter, 3/4 cup granulated sugar, 1/4 cup brown sugar
• Add the egg, eggnog, and vanilla extract to the butter-sugar mixture, and beat until well combined.
  1 egg, 1/3 cup eggnog, 1 teaspoon vanilla extract
• In a separate bowl, whisk together the flour, baking powder, nutmeg, and salt. Then add the dry ingredients to the wet ingredients and mix just until the flour mixture disappears.
  2 1/4 cups all-purpose flour, 1/2 teaspoon baking powder, 1/2 teaspoon nutmeg, 1/2 teaspoon salt
• Press the cookie dough into the prepared 8x8-inch pan, spreading it out evenly. Bake in the preheated oven for 25-27 minutes or until a toothpick inserted in the center comes out clean.

Make the frosting

• While the bars are cooling, prepare the frosting. In a large bowl, beat together the softened butter, powdered sugar, eggnog, and vanilla extract until light and fluffy.
  1/4 cup butter, 2 cups powdered sugar, 1/4 cup eggnog, 1/2 teaspoon vanilla extract
• Once the bars are completely cool, spread the frosting evenly over the top. Add a sprinkle of nutmeg, then chill in the fridge for a few minutes for the frosting to set before slicing into the bars and serving.
  A pinch of nutmeg