1pound(4 sticks) unsalted butter, very soft but not melted
4-6tablespoonselderflower liqueur
Instructions
In a small heavy saucepan, stir ¾ cup sugar and water and place over medium high heat. Stop stirring and wash down the sides of the saucepan using a pastry brush dipped in water to prevent crystals from forming.
In the bowl of an electric mixer, using the whip attachment, beat the egg whites on medium high speed until foamy.
Add cream of tartar and raise speed to high, beating until soft peaks form.
Gradually add the 4 tablespoons sugar and beat on high speed until stiff peaks form.
Raise the temperature of the sugar syrup to high and boil the syrup until a candy thermometer registers 240 degrees Fahrenheit.
Turn mixer to high speed and slowly pour the sugar syrup into the egg whites, making sure not to pour over the whip attachment.
Continue beating mixture on high speed until the bottom of the mixing bowl feels cool to the touch.
On medium high speed, add butter slowly. Mixture may appear curdled at first but will smooth out as more butter is added.
On low speed, slowly drizzle in liqueur.
Use immediately or refrigerate in a covered container for up to 5 days. Bring to room temperature and beat in the mixer to re-gain the proper consistency.