Buttercream Frosting

Combine the egg whites and salt in a very large mixing bowl.

Stir the water and 1 1/2 cups of sugar in a heavy medium saucepan until the sugar dissolves, then bring the syrup to a boil over medium heat, without stirring, brushing the sugar crystals down the side of the pan with a wet pastry brush. Boil until the syrup registers 238°F on a candy thermometer.

Meanwhile, beat the egg whites with an electric mixer at medium-high speed until frothy, then gradually add the remaining 2 tablespoons of sugar and beat at medium speed until the whites just hold soft peaks. With mixer on high speed, immediately but slowly pour the hot syrup in a thin stream down the side of the bowl and into the whites, beating constantly (avoid pouring it onto the beaters and the side of the bowl).

Beat, scraping down the side of the bowl with a silicone spatula, until the meringue is cool to the touch, about 10 minutes in a standing mixer or 15 with a handheld. (Meringue must be properly cooled before proceeding.)

With the mixer on medium speed, gradually add the butter 1 tablespoon at a time, beating well after each addition until well blended. Continue beating until the buttercream is smooth. The buttercream may look curdled before all of the butter is added but it will come back together. Scrape the vanilla bean seeds and add them to frosting; beat 1 minute more.

NOTE: Egg whites in this recipe are not cooked. If salmonella is a problem in your area, you can use reconstituted powdered egg whites such as Just Whites.