In a large bowl, cream butter and sugar until light and fluffy.
Stir in eggs, eggnog,cinnamon, nutmeg, baking powder and vanilla.
Gradually add flour a little at a time until just combined.
Chill dough for 30-60 minutes.
Preheat oven to 350 degrees F.
Drop by rounded teaspoon onto greased cookie sheets.
Bake for 15-18 minutes or until the edges are golden brown.
Cool completely.
For the Frosting
In a large bowl, cream butter until light and fluffy. Gradually add powdered sugar a little at a time. Add eggnog as needed until you reach your desired consistency.
Spread icing onto cookies, and sprinkle with nutmeg if desired.