Italian Meringue Buttercream

Combine ½ cup (100 g) granulated sugar with ¼ cup water in a small heavy saucepan; cook, without stirring, on medium-high heat until the mixture reaches 230°F on an instant-read or candy thermometer.

Meanwhile, whip 5 large egg whites in the bowl of a stand mixer fitted with the whisk attachment on medium speed until frothy. Slowly stream in the remaining ¼ cup (50 g) granulated sugar and beat the meringue until medium peaks form.

Continue heating the sugar mixture until it reaches soft-ball stage, 240°F. Reduce mixer to low speed and, with the mixer running, pour the hot sugar syrup into the meringue in a slow, steady stream. (Do the best you can to avoid pouring onto the sides of the bowl or the beater as the sugar will harden on contact.) Increase mixer to medium-high speed and whip until the meringue cools to room temperature and holds a stiff peak, 2–3 minutes.