Ingredients:

  • large egg whites (approx. 150g)
  • ¼ cups (250g) granulated sugar
  • ¼ teaspoon cream of tartar (optional)
  • ½ cups (340g) unsalted butter, very soft and room temperature
  • teaspoons pure vanilla extract
  • Pinch of fine sea salt

Instructions:

  1. Prepare Water Bath: Fill a saucepan with about 1 inch of water and bring to a gentle simmer (not a rolling boil).
  2. Combine & Heat: Place egg whites, sugar, and cream of tartar (if using) into the heatproof bowl. Set the bowl over the simmering water bath (ensure the bottom of the bowl doesn't touch the water).
  3. Whisk Until Dissolved: Whisk constantly and gently over the heat until the sugar is completely dissolved and the mixture reaches 160°F (71°C) on a thermometer. The mixture should feel perfectly smooth when rubbed between two fingers.
  4. Whip the Meringue: Immediately remove the bowl from the heat and transfer the mixture to the stand mixer bowl. Whisk on high speed until the meringue is stiff, glossy, and completely cool to the touch (the bowl should feel room temperature).
  5. Add Butter Gradually: Switch the mixer speed to medium-low. Add the softened, room-temperature butter, one tablespoon at a time, allowing each piece to incorporate fully before adding the next. Scrape down the sides often.
  6. Continue Mixing: The mixture may look curdled or soupy initially (this is normal). Continue mixing; the emulsion will eventually catch and stabilize.
  7. Final Whip and Flavour: Increase the speed to medium-high and beat for several minutes until the frosting becomes light, incredibly fluffy, and homogenous. Beat in the vanilla extract and salt.