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1
Special equipment: a candy thermometer
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Place the egg whites and 1/3 cup of the sugar in the bowl of an electric mixer fitted with a whisk attachment.
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Beat on medium-high speed until the egg whites reach the soft peak stage.
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4
Meanwhile, pour the remaining sugar and 1/3 cup water in a medium saucepan set over medium heat.
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Attach a candy thermometer to the side of the pan and bring to the soft-ball stage, without stirring, 240 degrees F.
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The egg whites and syrup should be ready at about the same time.
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If one is ready before the other then you can remove the pan from the heat or stop whipping for a few minutes.
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Continue to whip the egg whites on medium-high speed and slowly drizzle in the hot syrup, aiming the syrup between the side of the bowl and the beaters.
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9
Continue to whip until both the bottom of the bowl and the mixture are cool, 10 to 15 minutes.
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The mixture should be thick and will form firm peaks at this point.
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11
Beat in the salt.
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12
At this point you have an Italian meringue.
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13
While still beating on medium-high, add the butter, a few pieces at a time.
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As the butter is added, the buttercream may appear to thin out some, but it will thicken into firm peaks once all of the butter is added.
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15
Beat in the vanilla extract.
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If the buttercream is still too loose, beat on high speed until thickened.
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Use right away or refrigerate in an airtight container overnight.
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The buttercream may need to be beaten slightly to smooth out before using.
