Ingredients
1 cup sugar, divided1/4 cup water4 large egg whites, room temperature2 cups unsalted butter, cubed, room temperature1-1/2 teaspoons vanilla extract
Preparation
In a small heavy saucepan, combine 3/4 cup sugar and water. Bring to a boil; cook over medium-high heat until a thermometer reads 250° (hard-ball stage), 8 to 10 minutes. Meanwhile, using a stand mixer, beat egg whites in a large bowl on high speed until foamy. Gradually add remaining 1/4 cup sugar, 1 tablespoon at a time, beating on high after each addition until sugar is dissolved and soft peaks form.
Slowly pour hot sugar syrup over egg whites while beating continuously. Continue beating on high until mixture cools to room temperature, 15 to 20 minutes.
Gradually add butter, a few tablespoons at a time, beating on medium after each addition until smooth. Beat in vanilla.
