This rich, light-as-air frosting starts with an Italian meringue, the traditional name given to a meringue cooked with a hot sugar syrup. It creates a stable frosting with a silky texture that’s perfect for icing cakes or filling macarons. Start whisking the egg whites while the syrup is heating so that they’re foamy and light by the time the syrup reaches 245°; pouring the syrup in a thin stream down the side of the bowl will keep it from catching the whisk and splattering. Make sure that the meringue is cool to the touch before you begin adding the butter, so that you don’t melt it.
- 21 tbsp. unsalted butter, softened
- 1 tsp. vanilla extract
- 1 cup plus 1 tsp. granulated sugar
- 2 tsp. corn syrup
- 3 egg whites
- Beat butter and vanilla until smooth and creamy; set aside. Begin heating sugar and corn syrup with 1⁄4 cup water in a 1-qt saucepan over medium-high heat. Meanwhile, in the bowl of a stand mixer fitted with a whisk attachment, beat egg whites until frothy. When the syrup reaches 245° on a candy thermometer, slowly stream syrup down side of bowl, into egg whites while beating, avoiding the whisk. Continue beating egg whites on high speed until stiff peaks form and meringue is cool to the touch, about 5 minutes. Add butter and continue beating on medium speed until incorporated and smooth, about 2-3 minutes.