These crisp sugar cookies will lend a touch of whimsy to a birthday cake -- like our nautical Sailboat Cake -- but you can enjoy them anytime!
Sugar Cookies: In large bowl, sift together flour, baking powder, and salt.
With electric mixer, cream butter and sugar until fluffy. Beat in egg and vanilla.
Add flour mixture; mix on low speed to combine. Wrap in plastic; chill 1 hour.
Heat oven to 325 degrees. On lightly floured surface, roll dough 1/8 inch thick. Cut into fish shapes, 1 to 3 inches long, using a paring knife or cookie cutter. Transfer to ungreased baking sheets; chill until firm, about 30 minutes. Bake 10 to 12 minutes, until edges just begin to brown. Cool on wire racks.
Royal Icing: Beat meringue powder and scant 1/2 cup water in electric mixer on low. Add confectioners' sugar, scrape sides, and beat until soft peaks form, about 10 minutes. To thin icing for filling in shapes, or "flooding," add a little more water. Tint some icing with food coloring, if desired.
Decorate cookies with icing and sanding sugar.