From Martha Stewart Living, June 2016. Topping for Neapolitan Cupcakes
- 8 ounces strawberries (1½ cups) hulled and coarsely chopped
- 4 large egg whites room temperature
- 1¼ cups sugar
- 3 sticks unsalted butter, cut into tablespoons room temperature
- Purée strawberries in a blender (you should have about ¾ cup purée). Combine egg whites and sugar in a mixer bowl set over (not in) a pot of simmering water and whisk constantly until sugar is dissolved and mixture is warm. (It should feel completely smooth when rubbed between your fingertips).
- Transfer bowl to mixer fitted with the whisk attachment. Starting on low speed and gradually increasing to medium-high, beat until stiff, glossy peaks form. Continue beating until bottom of bowl is cool to the touch, about 15 minutes. Reduce speed to medium-low and beat in butter, a few tablespoons at a time, until combined. Scrape down sides of bowl. Slowly add strawberry purée, beating until combined. (If buttercream appears curdled, increase speed to medium-high and beat until smooth.) Buttercream can be stored at room temperature if used same day, or refrigerated in an airtight container up to 3 days, or frozen up to 1 month. Before using, bring to room temperature and beat on low speed in a mixer fitted with the paddle attachment until smooth again, about 5 minutes.