6 large egg yolks
1 cup sugar
1/4 cup water
1/4 cup freshly squeezed lemon juice
2 cups unsalted butter, softened
1/4 tsp. lemon extract
Have ready a greased 1-cup heatproof glass measure near the range. In a bowl beat the yolks with an electric mixer until light in color. Meanwhile, combine the sugar, water, and lemon juice in a small saucepan (preferably with a nonstick lining) and heat, stirring constantly, until the sugar dissolves and the syrup is boiling. Stop stirring and boil to the soft-ball stage (238 deg F.). Immediately transfer the syrup to the glass measure to stop the cooking. If using an electric hand-held mixer, beat the syrup into the yolks in a steady stream. Don't allow syrup to fall on the beaters or they will spin it onto the sides of the bowl. If using a stand mixer, pour a small amount of syrup over the yolks with the mixer turned off. Immediately beat at high speed for 5 seconds. Stop the mixer and add a larger amount of syrup. Beat at high speed for 5 seconds. Continue with the remaining syrup. For the last addition, use a rubber scraper to remove the syrup clinging to the glass measure. Continue beating until completely cool. Gradually beat in the butter and lemon extract. Place in an airtight bowl. Bring to room temperature before using. Rebeat if necessary to restore texture.