An egg white-based frosting has the fluffy look of buttercream but a lighter texture. It’s the star of our ethereal Four-Layer White Cake. Caveat: An electric mixer is a must. By hand, it would be Seven-Hour Frosting.
Step 1: Place the ingredients in a large heatproof bowl over a pot of simmering water, making sure that the bottom of the bowl does not touch the water.
Step 2: Grip the bowl with a towel to steady it and whip the ingredients on high with a handheld electric mixer. Once the sugar has dissolved and the egg whites have reached the safe-to-eat temperature of 160° F (you can check with a meat thermometer to be sure), about 2 minutes, remove from heat.
Step 3: Continue to whip until the frosting is thick and glossy and has tripled in volume, about 7 minutes. Let cool completely on the counter before icing a cooled cake. See the full seven-minute frosting recipe.