6 large egg whites
¼ teaspoon cream of tartar
2 ¼ cups granulated sugar
½ cup water
2 ½ cups unsalted butter at room temperature
2 teaspoons vanilla extract
½ teaspoon lemon extract
1 tablespoon lemon zest finely chopped
Combine the egg whites and cream of tartar in the bowl of an electric mixer fitted with a whisk attachment.
Combine the sugar and water in a medium saucepan. Heat over medium high heat stirring until the sugar dissolves. Then use a pastry brush and cool water to brush any sugar from the side of the pan. Clip a candy thermometer to the side of the pan and heat to 235° F.
Once 235° F is reached, beat the egg whites first on medium until foamy then on high until soft peaks. When the candy thermometer reaches 245° F slowly pour the sugar mixture into the egg whites while the mixer is on medium high. Once incorporated, raise the mixer to high and beat until the bowl is cool to the touch. Cool the meringue before adding the butter.
Into the cooled meringue add the butter a tablespoon at a time while beating on medium high. If your mixer begins to overheat, turn it off for a few minutes until it cools down. Continue beating in the butter a tablespoon at a time until all the butter is incorporated.
Beat in the extracts and the lemon zest. If the buttercream starts to split just keep beating until it comes back together.
Use to frost Lemon Chiffon Cake.