Mix egg whites and sugar in a *clean* metal mixing bowl, and place over a pot of simmering water on your stovetop. Whisk occasionally until it hits 160 degrees.

Move egg mixture to your stand mixer and whip on high (using the whisk attachment) until stiff peaks form, and mixture is relatively cool. While waiting, cut up the butter into chunks. Set aside.

When Meringue has reached the stiff peaks stage, switch to low speed and add the butter a chunk at a time.

Once butter is incorporated into the mix, turn speed back up to high and whip until you have a smooth buttercream.

It will go through some weird stages before this point - soupy, maybe curdled. Don’t worry! It will come together!

Once everything has come together in a smooth buttercream, add your vanilla, and/or whatever other flavours you want. Mix on low until incorporated.