Combine flour, baking powder and salt on sheet of waxed paper.
Beat butter and sugar in bowl with mixer until smooth, 2 minutes. Beat in egg, rind and juice until fluffy, 1 minute. Gradually beat in flour mixture on low, or by hand, until a stiff dough forms. Divide in half. Flatten each into 6-inch square; wrap in plastic. Refrigerate 2 hours or overnight. Let stand at room temperature 15 minutes for rolling.
Heat oven to 350 degrees F. Coat baking sheets with cooking spray. Lightly flour dough. Roll half of dough on lightly floured surface to 1/4-inch thickness. Cut out into shapes, using cutters. Reroll scraps; cut out shapes to use all dough. Place cookies, 1 inch apart, on baking sheet. Repeat with other half of dough.
Bake in 350 degree F oven 8 to 10 minutes or until lightly golden around edges. Remove to rack to cool.a time, until consistency of sour cream. Use thicker half of icing for
Using small fine-tipped paintbrush, coat cookies with thinned Royal Icing. Let stand until dry. Decorate with thicker icing, piping with pastry bag fitted with fine writing tip. Divide icing in half. To make base coat for glaze: Thin half of icing with water, a drop at a time, until consistency of sour cream. Use thicker half of icing for piping. Tint icing with food colors as desired. Keep icing covered when not using. Make additional icing as needed for decorating cookies.
Beat together meringue powder or powdered egg whites, confectioners sugar, and water in bowl until peaks form, 10 minutes.