Fresh Strawberry Buttercream

From Martha Stewart Living, June 2016. Topping for Neapolitan Cupcakes

Ingredients

• 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

Instructions

1. 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).
2. 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.