Lemony Swiss Meringue Buttercream

Use this buttercream to frost "Whisk Kid" blogger Kaitlin Flannery's colorful Rainbow Cake.

  • Yield: Makes enough for one 9-inch-round six-layer cake

Source: The Martha Stewart Show, April 2010


For the Filling and Crumb Coat

  • 9 large egg whites
  • 1 3/4 cups sugar
  • 2 cups (4 sticks) unsalted butter, cut into small pieces, room temperature
  • 2 teaspoons pure lemon extract

For the Frosting

  • 5 large egg whites
  • 1 cup sugar
  • 1 cup (2 sticks) unsalted butter, cut into small pieces, room temperature
  • 1 teaspoon pure lemon extract


  1. Make the filling and crumb coat: Cook egg whites and sugar in a small saucepan over medium heat, whisking constantly until sugar is completely dissolved. Transfer to the bowl of an electric mixer fitted with the whisk attachment; mix on high speed until mixture is room temperature. With the mixer on medium-low, add butter, one piece at a time, mixing well after each addition.

  2. Remove whisk attachment and switch to paddle attachment. Increase speed to high and beat until buttercream comes together, about 5 minutes; beat in lemon extract.

  3. Make the frosting: In a clean saucepan and bowl of an electric mixer, repeat process in step 1.


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