Italian Meringue Buttercream
To make the sugar syrup, place the candy thermometer in the saucepan and heat the water and 120 g of sugar over medium-high heat. Partially cover with a lid to capture the evaporating water this helps to moisten the sides of the saucepan to prevent sugar crystals from forming.
With the mixer on high speed, begin whipping the egg whites to stiff peaks. When the peaks are stiff, with the mixer still running slowly pour the remaining sugar into the meringue.
Raise the heat under the sugar syrup to bring the syrup to 245°F, if it is not there already. When the syrup is at 245°F, remove the thermometer and slowly pour the syrup into the meringue.
After 1 to 2 minutes reduce the mixer speed to medium for 3 to 4 minutes, or until the meringue is cooled. Add the butter 1 tablespoon at a time. Increase the mixer speed to high for 1 to 2 minutes, or until the butter is fully incorporated.