Step 1

Combine the sugar and water in a saucepan over medium heat. As soon as the sugar is dissolved, stop stirring and increase the heat to high. Bring the mixture to a boil until a candy thermometer reaches 240 F (115 C).

Step 2

Meanwhile, place the egg whites in the bowl of a stand mixer fit with the whisk attachment. When the sugar reaches 200 F (93 C), begin whipping the egg whites on high speed.

Step 3

As soon as the sugar reaches 240 F (115 C), carefully and slowly begin streaming the sugar into the mixer down the side of the bowl while it is still running. Add the salt. Continue beating to stiff peaks and until the meringue has cooled to room temperature.

Step 4

While the mixer is still running, add the butter in 1 tablespoon at a time until it is all incorporated and the buttercream is smooth and fluffy. It is common for the buttercream to start looking broken during this time. You might think it is ruined, but trust in the process. Keep adding the butter a little at a time and keep whipping. It will come back together into a silky smooth buttercream.