Cut butter into small 1/2 inch cubes and set aside for later.

Be sure to separate your eggs so you have the 6 egg whites above. Make sure no remnants of egg yolk appear in the egg whites, otherwise they won’t whip up nicely.

In a (heatproof) bowl of an electric stand mixer, combine the egg whites and sugar and mix by hand until combined.

Set the egg-sugar bowl on top of the pot and reduce the heat to medium-low.

Whisk the egg-sugar mixture often, until the sugar has dissolved, about 3-5 minutes. Touch the mixture between your thumb and pointer finger to feel for any sugar granulated. It should be fully dissolved once ready.

Remove the bowl of egg-sugar mixture from the pot and carefully dry the bottom of the bowl with a towel.

Transfer the bowl to the stand mixer fitted with a whisk attachment and beat the egg mixture for 10-15 minutes on medium-high speed until stiff peaks form. It will look like a shiny, glossy meringue.

Once the meringue has stiff peaks, and the bowl is no longer warm, continue to the next steps.

Switch the mixer to a fitted with a paddle attachment.

Add 3-4 cubes of butter at a time to the whipped meringue, beating on medium-high speed. Be sure to let the butter combine into the meringue before adding a few more cubes of butter. Repeat until all the butter has been incorporated and a thick, creamy buttercream forms.

Beat for 5-7 minutes until thick and stiff. If the mixture becomes curdled, step away and keep beating the buttercream. If the mixture still looks curdled after 5-8 minutes of whipping it, pause and set the bowl in the fridge for 10 minutes, then return it to the mixer and mix again.

Beat in the vanilla and salt until just combined.