1-Clean all tools thoroughly with lemon juice or white vinegar to remove grease.

2-Separate egg whites one at a time into a large heatproof bowl.

3-Whisk sugar into egg whites, then place the bowl over simmering water and whisk constantly until the sugar dissolves and the mixture reaches 160°F (71°C) or feels smooth without granules.

4-Transfer the warm mixture to a stand mixer with a whisk attachment and beat on medium-high speed until stiff glossy peaks form and the mixture is cool to the touch, about 10-15 minutes. If stiff peaks aren’t achieved, refrigerate the bowl uncovered for 10 minutes first.

5-Once cooled to room temperature (around 70°F/21°C), switch to the paddle attachment and add butter one tablespoon piece at a time on medium-high speed, waiting for full incorporation before adding the next.

6-Add vanilla extract and salt, then beat on medium speed for about 30 seconds until smooth.

7-For troubleshooting, if the mixture is curdled or too thick, warm the bowl briefly over simmering water until the edges liquefy, then beat again until smooth. If it’s too thin or soupy, chill the bowl in the refrigerator in 20-minute increments, then beat until thickened.