In a double boiler, mix the egg whites and sugar together. Place over medium heat so the water is simmering – not boiling.

Cook the egg whites and sugar t5 ogether until the sugar has completely dissolved about 3-5 minutes. This usually happens when the mixture turns 160 degrees.

Pour the mixture into a standing mixer fitted with the whisk attachment. Beat on low until the mixture becomes frothy. Turn up the speed slowly until the mixer is on high. Continue to whisk the meringue until glossy stiff peaks occur. The meringue should be at room temperature at this time. If it’s not, wait a few minutes before the next step.

Add in the butter one tablespoon at a time while the mixer is on low/medium speed. The mixture will start to deflate and then turn lumpy. Add in the vanilla. Continue to whip on high once the butter is all incorporated for another minute or two.

Remove the whisk attachment and place on a paddle attachment (one with a spatula end is preferred but not necessary). Mix on low to release the trapped air until a smooth and glossy buttercream appears.