Mix flour, baking powder and salt.
Beat butter and sugar in bowl until smooth, 2 minutes. Beat in egg until fluffy, 1 minute. On low, beat in flour mixture until stiff dough forms. Divide in half; flatten each half. Wrap; refrigerate 2 hours or overnight. Let stand at room temperature 15 minutes before rolling.
Heat oven to 350 degrees F. Coat baking sheets with cooking spray. Flour dough. Roll out half, 1/4 inch thick. Cut out shapes using cutters. Reroll scraps. Place cookies, 1 inch apart, on sheets. Repeat with other half.
Bake in 350 degree F oven 8 to 10 minutes, until golden around edges. Remove to racks to cool.
With small paint- brush, coat cookies with thinned Royal Icing. Let dry. Pipe on thicker icing. Makes about 36 (3-inch) cookies.
Beat meringue powder, confectioners sugar and water in bowl until peaks form, 10 minutes (about 3 cups). Divide icing in half. For base coat: Thin half of icing with water, a drop at a time, until consistency resembles honey. Use thicker half for piping. Tint icing with food colors.