To make the strawberry Swiss meringue puree the strawberries in a food processor, leaving some small chunks; set aside.

Combine the egg whites and sugar in the heatproof bowl of a stand mixer over a pan of simmering water. Whisk constantly by hand until the mixture is warm to the touch and the sugar has dissolved (the mixture should feel completely smooth when rubbed between your fingertips).

Place the bowl in the stand mixer fitted with the whisk attachment. Mix until stiff peaks form. Continue mixing until the mixture is fluffy and glossy, and completely cool (test by touching the bottom of the bowl), about 10 minutes.

Reduce the mixer speed to medium-low and add the butter a few tablespoons at a time, mixing well after each addition.

Once all the butter has been added, scrape down the sides of the bowl with a spatula and switch to the paddle attachment; continue beating on low speed until all air bubbles are gone, about 2 minutes.

Add the strawberry puree and beat until combined. Use to frost a 2 layer 8-inch cake or 24 cupcakes.