Yield: 3 1/2 cups (enough for one 9-inch, 2-layer cake, or a 9-by-13-inch sheet)

Cook’s notes: Your life will be easier if you use an instant-read thermometer and a stand mixer, but neither are necessities. This can be chilled for a week, or frozen; thaw overnight in the refrigerator before re-whipping until smooth. See the variations at the end of the recipe for flavorings.

4 large egg whites

3/ 4 cup granulated sugar

1/ 4 teaspoon cream of tartar

Pinch of salt

1 1/ 2 cups (3 sticks) unsalted butter, softened (see step 2)

1 teaspoon vanilla

Bring a saucepan filled with a few inches of water to a simmer. In a large metal mixing bowl, whisk together egg whites and sugar. Place over saucepan, being sure water doesn’t touch the bottom of the bowl. Whisk constantly until whites are warm and the sugar dissolves; if you have a thermometer, this should be between 120 degrees and 130 degrees. Remove from the heat, add the cream of tartar and salt, and beat the whites with an electric mixer on medium-high speed for 7 to 10 minutes, until the whites form a very thick meringue that is cool to the touch. Be sure both the meringue and the bowl are cool, to avoid melting the butter.
Check the butter; it should feel cool, not cold, and be slightly malleable. (If it’s too cold, the buttercream could separate; should this happen, heat it very briefly — just a few seconds over simmering water, then re-beat until it comes together.) If you have a thermometer, it should register about 68 degrees.
While continuing to beat the meringue on medium-high speed, add 2 tablespoons butter at a time, whipping after each addition. This will deflate the meringue at first, but it will fluff up by the end. When all the butter is added, add the vanilla and beat briefly to blend. Use immediately or chill; if buttercream seems too soft to use immediately, chill for 5 to 10 minutes and rewhip briefly.

Variations: Add 2 tablespoons of liqueur with the vanilla. For chocolate buttercream, melt and cool completely 4 to 6 ounces of good-quality semisweet chocolate; whip 1 cup of the finished buttercream into the chocolate to blend it well, then add that to the remaining buttercream and whip to blend well. For a citrus buttercream, beat in with the vanilla 2 tablespoons grated orange or lemon zest (or combine the two), plus 1 teaspoon orange or lemon extract, or an additional tablespoon of an orange liqueur such as Grand Marnier. For a coffee buttercream, dissolve 1 tablespoon of instant espresso powder in 1 tablespoon coffee liqueur, hot coffee, or hot water; add to buttercream with the vanilla. Combine the coffee and chocolate additions for a mocha frosting.

One Response to “Swiss Meringue Buttercream”

  1. […] answer, I discovered thanks to this recipe, is 68 degrees.  I will never again make buttercream without an instant read thermometer in hand. […]