In a large bowl, cream together butter and sugar until smooth.
Beat in eggs and vanilla.
Stir in the flour, baking powder, and salt. Cover, and chill dough for at least one hour (or overnight).
Preheat oven to 400 degrees F (200 degrees C).
Roll out dough on floured surface 1/4 to 1/2 inch thick.
Cut into shapes with any cookie cutter.
Place cookies 1 inch apart on ungreased cookie sheets. Bake 6 to 8 minutes in preheated oven.
Cool completely.
For the Icing:
I used a standard Royal Icing recipe Which called for 2.5 cups of powdered sugar, 2 egg whites, 1 tablespoon vanilla, 1/4 teaspoon cream of tartar a bit of water and food coloring.
Sift the dry ingredients into a bowl.
Stir in the egg whites and beat until smooth.
Add the vanilla and beat until combined. And add water 1/2 a teaspoon at a time until you reach the desired consistency.
Add food coloring and stir! Allow to rest for 20+ minutes so air bubbles can escape.
To flood the cookies you pipe an outline onto the cooled cookie.