Swiss Meringue Buttercream Frosting (Martha Stewart)

SWISS MERINGUE BUTTERCREAM

"If there is one frosting recipe a home baker should always have on hand, this is it. This all-purpose buttercream has an ultra-silky, stable texture that spreads beautifully over cakes and cupcakes, and can be piped into perfect peaks and patterns. Swiss meringue buttercream is also less sweet than other types of frosting, with a wonderful buttery taste. It can be varied with different extracts, juices, zests, and other flavoring agents, and tinted any shade. Don't worry if the mixture appears to separate, or "curdle," after you've added the butter; simply continue beating on medium-high speed, and it will become smooth again."

5 large egg whites
1 cup plus 2 tablespoons sugar
Pinch of salt
1 pound (4 sticks) unsalted butter, cut into tablespoons, room temperature
1 1/2 teaspoons pure vanilla extract

Combine egg whites, sugar, and salt in the heatproof bowl of a standing mixer set over a pan of simmering water. Whisk constantly by hand until mixture is warm to the touch and sugar has dissolved (the mixture should feel completely smooth when rubbed between your fingertips).

Attach the bowl to the mixer fitted with the whisk attachment. Starting on low and gradually increasing to medium-high speed, whisk until stiff (but not dry) peaks form. Continue mixing until the mixture is fluffy and glossy, and completely cool (test by touching the bottom of the bowl), about 10 minutes.

With mixer on medium-low speed, add the butter a few tablespoons at a time, mixing well after each addition. Once all butter has been added, whisk in vanilla. Switch to the paddle attachment, and continue beating on low speed until all air bubbles are eliminated, about 2 minutes. Scrape down sides of bowl with a flexible spatula, and continue beating until the frosting is completely smooth.

Keep buttercream at room temperature if using the same day, or transfer to an airtight container and refrigerate up to 3 days or freeze up to 1 month.

Before using, bring to room temperature and beat with paddle attachment on low speed until smooth again, about 5 minutes.

(OPTIONAL) TO TINT BUTTERCREAM (OR ROYAL ICING):
Reserve some for toning down the color, if necessary. Add gel-paste food color, a drop at a time (or use the toothpick or skewer to add food color a dab at a time) to the remaining buttercream. You can use a single shade of food color or experiment by mixing two or more. Blend after each addition with the mixer (use the paddle attachment) or a flexible spatula, until desired shade is achieved. Avoid adding too much food color too soon, as the hue will intensify with continued stirring; if necessary, you can tone down the shade by mixing in some reserved untinted buttercream.

Makes about 5 cups
Source: Martha Stewart's Cupcakes by Martha Stewart Living Magazine