3 egg whites, room temperature
1/2 cup (100 grams) sugar
1/8 teaspoon cream of tartar
1/2 teaspoon vanilla extract

Combine sugar, egg whites, and cream of tartar in a medium bowl set over a pot filled with a couple of inches of barely simmering water. Whisk the mixture frequently to prevent the egg whites from cooking. Continue whisking until the mixture reaches 160 degrees. Remove the bowl from the heat and whisk the mixture on high until it is shiny and stiff peaks form, then stir in vanilla extract.