optional: liqueur of your choice--just a splash or two; you don't want your buttercream to be too loose.
Instructions
Bring the sugar and water to a boil in a small saucepan. Cover with a lid or plastic wrap and let boil for 2-3 minutes. Remove the lid and cook the sugar to 244 degrees, F.
While your syrup is boiling, whip the whites and salt on medium speed of your stand mixer to soft peaks. This is a timing issue, so watch them carefully. If you overbeat your whites before your syrup reaches temperature, they'll be grainy and dumb. Adjust the speed of the mixer up or down and try and get your whites to the perfect consistency at the same time your sugar reaches 244F.
When the syrup is ready, with mixer on medium low, pour syrup in a thin stream down the inside of the mixing bowl. This will give the syrup a chance to cool off a bit as well as keeping the syrup from getting spun all over the sides of the mixer by the whisk attachment.
Turn mixer to high and whip until whites are completely cool and hold firm peaks.
Add the softened butter, a bit at a time making sure one addition is blended in before adding the next.
Beat in vanilla or flavoring of your choice.
Notes
For chocolate Italian buttercream, whisk in 6 oz. melted and cooled semisweet or bittersweet chocolate after all the butter is incorporated.You can also add unsweetened fruit puree to change up the flavor and color. Consider flavoring with citrus zest, ground spices like cinnamon or cardamom, or with interesting extracts like maple or coffee.