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.
In the bowl of your electric mixer (or with a hand mixer), beat the egg whites with the lemon juice until combined. Add the sifted powdered sugar and beat on low speed until combined and smooth.
The icing is the right consistency to cover or “flood” sugar cookies when you lift the beater and the ribbon of icing that falls back into the bowl remains on the surface for a few seconds before disappearing. Another test is to take a cookie and place a small amount of icing in the center of the cookie. Using a small knife, push the icing to the edge of the cookie. If the icing runs off the edge, thicken the icing by adding a little more confectioners sugar. Conversely, if the icing is too thick, add a little water.
For each color of icing, place ½ cup icing in a bowl and stir in 3 – 4 drops of food color until evenly distributed. Add additional drops until icing is of desired color.
The icing needs to be used immediately or transferred to an airtight container as royal icing hardens when exposed to air. Cover with plastic wrap when not in use.
Makes about 3 cups.
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