1. Preheat oven to 350°.
2. To prepare cake, weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour, 1/2 teaspoon salt, baking soda, and baking powder. Place 1/2 cup butter and 1 1/4 cups sugar in a large bowl; beat with a mixer at high speed until well blended. Add egg yolks, 1 at a time, beating well after each addition. Stir in vanilla extract. Reduce mixer speed to low. Add the flour mixture and buttermilk alternately to butter mixture, beginning and ending with flour mixture, and beat just until combined. Using clean, dry beaters, beat 3 egg whites and 1/4 teaspoon cream of tartar at high speed until stiff peaks form. Fold one-third of egg whites into batter. Gently fold in the remaining egg whites.
3. Line 24 muffin cups with cupcake liners; coat with baking spray. Spoon batter into cups. Bake at 350° for 23 minutes or until a wooden pick inserted into centers comes out with moist crumbs clinging. Cool in pans 10 minutes. Remove from pans; cool completely on wire racks.
4. To prepare frosting, place 1 cup sugar, 1/4 cup water, and vanilla bean in a saucepan; bring to a boil. Without stirring, cook 3 minutes or until a candy thermometer registers 250°; discard vanilla bean. Combine 3 egg whites, 1/4 teaspoon cream of tartar, and 1/8 teaspoon salt in a large bowl; using clean, dry beaters, beat with a mixer at high speed until foamy. Pour hot sugar syrup in a thin stream over egg whites, beating at high speed until stiff peaks form. Reduce mixer speed to low; continue beating until mixture cools (12 minutes).
5. Beat 1/4 cup butter until light and fluffy, if desired. Fold in 1 cup egg white mixture. Fold butter mixture into remaining egg white mixture, stirring until smooth. Top cupcakes with frosting.
Note: Nutritional analysis includes butter.
VARIATION 1: Chocolate Cupcakes
Prepare Vanilla Cupcakes, decreasing the cake flour to 7 ounces (about 1 3/4 cups). Stir 1/2 cup unsweetened cocoa into flour mixture. Increase sugar to 1 1/2 cups. Decrease vanilla to 1/2 teaspoon. Melt 2 ounces unsweetened baking chocolate, and stir into batter after adding flour mixture and buttermilk. Prepare Vanilla Bean Frosting, increasing sugar to 1 1/3 cups and increasing water to 1/3 cup. Omit butter. Fold 1/4 cup unsweetened cocoa into meringue. Shave 1 ounce bittersweet chocolate over frosted cupcakes. SERVES 24 (serving size: 1 cupcake) CALORIES 185; FAT 6.6g (sat 3.9g); SODIUM 151mg
Proper Chocolate Shavings: Use a block or bar of good chocolate for your garnish of chocolate curls. If you rub your thumb over the surface two or three times and then shave, the curls will be less brittle and less likely to crack and break.
VARIATION 2: Red Velvet Cupcakes
Prepare Vanilla Cupcakes, adding 1/4 cup unsweetened cocoa to cake flour mixture. Stir 1 (1-ounce) bottle red food coloring into batter. Omit the Vanilla Bean Frosting. Place 3 tablespoons butter and 1 (8-ounce) block 1/3-less-fat cream cheese in a large bowl, and beat with a mixer at medium-high speed until smooth. Add 2 cups powdered sugar, 1/4 teaspoon vanilla, and 1/8 teaspoon salt; beat until smooth. Add red food color paste to icing; stir. Place frosting in a zip-top plastic bag; seal. Snip a 1/4-inch hole in 1 corner of bag. Pipe on top of cupcakes. SERVES 24 (serving size: 1 cupcake) CALORIES 201; FAT 8.4g (sat 4.9g); SODIUM 186mg
Stylish Swirls: Dot the thick frosting with a few drops of red food color paste, and stir gently to give it a swirled appearance. Carefully spoon into a zip-top bag, and pipe out.