Sift the cake flour, baking powder and salt into a bowl; set aside. Beat the butter and sugar in a large bowl with a mixer on medium-high speed until light and fluffy, about 5 minutes. Add the egg and vanilla; beat until incorporated. Reduce the mixer speed to low and beat in the flour mixture in 2 batches until just incorporated. Divide between 2 pieces of plastic wrap; shape into disks. Wrap and refrigerate until firm, at least 1 hour.
Line 2 baking sheets with parchment paper. Working with 1 disk at a time, roll out the dough on a floured surface until about inch thick. Cut out shapes with cookie cutters; arrange 2 inches apart on the prepared baking sheets. (If the dough becomes soft, refrigerate until firm.) Refrigerate the cookies 30 minutes. Gather the scraps and refrigerate until firm; reroll and cut out more cookies.
Position racks in the upper and lower thirds of the oven and preheat to 350 degrees F. Bake, switching the pans halfway through, until the cookies are slightly puffed and just golden, 13 to 15 minutes. Let cool 5 minutes on the baking sheets, then remove to racks to cool completely before icing.
Basic Royal Icing
Whisk one 1-pound box confectioners' sugar and 2 tablespoons meringue powder in a large bowl. Add 5 tablespoons water and beat with a mixer on medium-high speed until soft glossy peaks form, adding up to 1 more tablespoon water if necessary. If not using the icing right away, cover the bowl with a damp paper towel and plastic wrap to prevent it from drying out. (Makes about 2 1/4 cups.)
Striped:Spread royal icing on the cookie using a small offset spatula. Let set slightly, then dip a wooden skewer in tinted icing to draw stripes.
Pearled: Spread royal icing on the cookie using a small offset spatula. Let set slightly, then place sugar pearls around the edges.
Windowpane: Spread tinted royal icing on the cookie using a small offset spatula. Let set slightly, then dip a wooden skewer in white icing to draw crisscross lines.
Ombre: Tint half of the royal icing, then mix one-third of the tinted icing with one-third of the white icing. Spread the 3 shades on the cookie from dark to light, blending the sections.
Floral: Spread royal icing on the cookie using a small offset spatula. Dip a wooden skewer in different colors of tinted icing to draw dots for flowers. Photograph by Jeff Harris/Studio D
Recipe courtesy of Hollis Johnson for Food Network Magazine