Creamiest Peanut Butter Icing

Combine sugar, egg whites, and salt in a bowl and place over simmering water (I used the bowl of my stand mixer or just use a heat proof bowl). Whisk gently but constantly and heat the mixture until slightly thickened and an instant read thermometer registers at 350 degrees (about 3 minutes).

Place the bowl back on the stand mixer fitted with the whisk. Beat the mixture at medium speed until the consistency of shaving cream and slightly cooled, about 2 minutes. Add butter one piece at a time until smooth and creamy (if it starts to look curdled, just keep adding butter). Once all butter is added, add peanut butter and vanilla extract. Beat on high until light and fluffy. I had to put mine in the fridge for a little, too, so that it thickened up.