Foolproof Swiss Meringue

Bring 2 cups of water to a simmer in a medium pot.

Combine sugar, egg whites, salt, and cream of tartar in the bowl of a stand mixer.

Reduce the heat under the simmering water and place the stand mixer bowl over the steam. Whisk egg whites lightly until a digital or candy thermometer inserted into the mixture reads 160 degrees F (71 degrees C), 6 to 10 minutes. Remove from the heat immediately.

Place the bowl onto the stand mixer and attach the whisk attachment. Whisk on high speed until egg whites are cool and stiff peaks form, about 3 minutes; the mixture should hold peaks effortlessly and start balling up around the whisk attachment while appearing silky, shiny, and pure white.

Use meringue immediately.