Italian Meringue Buttercream
So versatile it can be used as a base for many other buttercreams. The photo above actually has lemon curd mixed into it. This is one of my favorite frostings. It has everything this baking girl can want in a frosting… creamy, silky, buttery taste.
Makes 4 ½ cups
1 ¼ cups sugar
2/3 cups water
5 large egg whites
Pinch of cream of tarter
1 pound (4 sticks) unsalted butter, chilled
1 tsp. pure vanilla extract
In a small saucepan over medium heat, bring sugar and 2/3 cup of water to a boil. Continue boiling until syrup reaches 238˚ on a candy thermometer (soft-ball stage).
Meanwhile, place egg whites in the bowl of a standing mixer fitted with the whisk attachment, and beat on low speed until foamy. Add cream of tartar, and beat on medium-high speed until stiff but not dry. Do not over beat.
With mixer running, add syrup to whites in a stream, beating on high speed until no longer steaming, about 3 minutes. Add butter bit-by-bit, beating until spreadable, 3 to 5 minutes; beat in vanilla. If icing curdles, keep beating until smooth.
Source Martha Stewart