Source: The Martha Stewart Show, Episode 5128
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
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.
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.
Make the frosting: In a clean saucepan and bowl of an electric mixer, repeat process in step 1.