Preheat oven to 300ºF. In a medium bowl combine flour, baking powder, cinnamon and nutmeg. Mix well with a wire whisk and set aside. In a large bowl cream sugar and butter with an electric mixer to form a grainy paste. Add eggnog, vanilla and egg yolks and beat at medium speed until smooth. Add the flour mixture and beat at low speed just until combined. Do not overmix. Drop by rounded teaspoons onto ungreased baking sheets, 1 inch apart. Sprinkle lightly with nutmeg. Bake for 23 to 25 minute or until bottoms turn light brown. Transfer to cool, flat surface immediately with spatula.