1. Preheat oven to 350°.
2. To prepare cookies, weigh or lightly spoon flour into dry measuring cups, and level with a knife. Combine flour, 1/2 teaspoon salt, and baking powder, stirring with a whisk. Place butter and granulated sugar in a large bowl, and beat with a mixer at high speed until light and fluffy. Add egg, and beat until well blended. Beat in vanilla extract. Reduce mixer speed to low. Add the flour mixture to butter mixture; beat just until combined.
3. Shape dough into a 4-inch round, and cover with plastic wrap. Chill for 1 hour. Roll dough to 1/4-inch thickness on a lightly floured surface. Cut out 40 (2 x 3-inch) cookies, rerolling scraps as necessary. Place cookies 1 inch apart on a baking sheet lined with parchment paper. Bake at 350° for 9 minutes or until lightly browned on bottoms. Cool on a wire rack.
4. To prepare icing, combine powdered sugar, egg white powder, and 1/8 teaspoon salt, stirring well. Gradually add 2 tablespoons water, stirring constantly with a whisk until smooth. Decorate cookies as desired. Sprinkle with sugar, if desired. Let the cookies stand on a cooling rack until icing is completely dry (about 1 hour).
VARIATION 1: Gingerbread Cookies
Prepare Iced Sugar Cookies, increasing flour to 11.25 ounces (about 2 1/2 cups). Stir 1 tablespoon ground ginger, 1 teaspoon ground cinnamon, 1/2 teaspoon ground cloves, and 1/4 teaspoon ground allspice into flour mixture. Add 1/4 cup molasses to dough when vanilla is added. Halve icing recipe; decorate as desired. SERVES 40 (serving size: 1 cookie) CALORIES 91; FAT 3.7g (sat 2.2g); SODIUM 63mg
Finishing flourishes don't require special equipment. First, “flood” cookies by spreading thin frosting with a small offset spatula to coat, if desired. Pipe thicker frosting from a zip-top bag to outline. Use a toothpick to make small dots of icing that act as glue for decorative details like sugar pearls.
VARIATION 2: Pecan Cookies
Prepare Iced Sugar Cookies, decreasing the butter to 10 tablespoons. Stir 3/4 cup chopped, toasted pecans into dough. Omit icing. Dust cooled cookies with 1/3 cup powdered sugar. SERVES 40 (serving size: 1 cookie) CALORIES 82; FAT 4.5g (sat 2g); SODIUM 54mg
Dust cookies with a bit of powdered sugar for a finishing touch that's not too sweet. Place sugar in a fine sieve, and shake it over cooled cookies.