RECIPE PREP: Make double sure the metal bowl and whip are completely free of grease.* These kitchen tools must be meticulously clean. If there’s even a tiny speck of grease, it will prevent the egg whites from whipping.

1. Create a “makeshift” double broiler. Add a few inches of water to a medium saucepan – the pan must be large enough to suspend the heat-proof metal bowl from your stand mixer. Bring the water to a simmer on stovetop over medium-low heat.
2. Place the metal bowl over the simmering water. Make sure the water does not touch the bottom of the bowl. Add egg whites and sugar to the bowl. Whisk constantly until the sugar has dissolved and mixture has reached 160ºF on an instant-read thermometer (about 5 minutes).
3. With kitchen towels to protect your hands from heat, carefully move the metal bowl from the stovetop to the stand mixer. Connect it with the paddle attachment. Beat on medium speed until stiff peaks form (about 5 minutes).
4. Turn the mixer to low speed. Slowly add the vanilla extract and marshmallow fluff. Turn the mixer to high speed. Whip the mixture until stiff peaks form again, about 3 minutes. (If the frosting is too sweet add a tiny pinch of salt.) The texture should be thick, glossy and luxurious.
5. If desired, transfer marshmallow frosting to a piping bag fitted with your favorite metal tip. Frost desserts as desired.