How to Make Swiss Meringue Buttercream Frosting

[Photographs: Vicky Wasik. Video: Natalie Holt]

Swiss meringue buttercream is the fastest and easiest frosting around, made from an ingredient so humble it's often just thrown away: leftover egg whites. They're cooked over a water bath, whipped into an airy meringue, then enriched with butter, for a silky-smooth frosting that tastes light and mild—a blank canvas waiting for your creative touch. Peanut butter? Melted chocolate? Vanilla beans? Ground peanut brittle? Freeze-dried fruit? Sure thing! Mix in whatever you like, and Swiss buttercream will make it the star.

One thing to note is that Swiss meringue is commonly made with too little sugar and not enough heat, producing something that's eggy, fragile, and raw. From there, adding butter only makes it greasy and dense, a frequent gripe among detractors of SMBC (as it's called online). If you joined me on my quest for the perfect meringue pie last year, you know that I've spent a not-insignificant amount of time tinkering with Swiss meringue to overcome those common complaints.

You can check out my full report here, but the short story is this: With a bit more sugar and a higher target temperature, Swiss meringue loses its eggy flavor and whips up stable, light, and fully cooked (the traditional advantages of an Italian meringue). If Swiss meringue starts with toasted sugar and vanilla bean, it can also be remarkably delicious.

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It's a rock-solid foundation for buttercream as is, but a few extra tweaks make it all the more outstanding. Bumping up the sugar, salt, and vanilla in my Swiss meringue ensures that its flavor and sweetness aren't overpowered by the butter. In turn, the added sugar offsets the butter's richness, so the finished product feels lighter than recipes that call for less. That additional sugar does require the meringue to be cooked to a higher temperature, but aside from that adjustment, the technique stays the same.

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If you haven't made a Swiss meringue before, the process is simple. Combine egg whites, toasted sugar, cream of tartar, salt, and vanilla seeds in a double boiler, and cook, stirring constantly with a flexible spatula. For this recipe, you'll take the mixture to about 185°F (85°C) to make sure it's fully cooked. Then you'll whip it on high speed until the meringue is fluffy, light, and cool to the touch, about 90°F (32°C).

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Sure, 90°F doesn't sound cool, but it's well below body temperature, so the bowl won't feel warm against your palm. It's also the perfect temperature to accommodate the butter, which should be pliable and cool, about 65°F (18°C). Whipped together, they'll average out to about 72°F (22°C).

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You can achieve that perfect temperature any number of ways, with a cooler meringue and warmer butter, or vice versa, but that's a tightrope beginners needn't walk. Though you have a few degrees of wiggle room in either direction, if the ingredient temperatures aren't properly balanced, the buttercream may be runny and thin, or dense and greasy—maybe even curdled and broken. With an awareness of the role temperature has to play, and a trusty digital thermometer, all those problems simply cease to exist. (If you're in the market for a thermometer, mine's a Polder. The clip-on attachment, heat-safe cord, and temperature alert make it ideal for a wide range of desserts, plus savory projects, too.)

Freshly made Swiss buttercream has the ideal consistency for frosting cakes and cupcakes, but it can also be kept in short- or long-term storage—a fact I rely on to polish off the egg whites left over from other baking projects. Simply roll open the mouth of a gallon-sized, heavy-duty zip-top bag; scrape in the buttercream; press out the air; and seal. It'll keep about two weeks in the fridge, or several months in the freezer. (The issue with freezing for longer than that isn't spoilage so much as odor absorption.) Do be sure to lay the bag flat, which helps the buttercream to thaw rapidly down the line. When you're ready to frost a cake, warm the buttercream back to 72°F, then re-whip to restore its spreadably soft consistency.

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With toasted sugar, loads of vanilla, and a drop of almond extract, my Swiss meringue buttercream tastes more satisfying than traditional recipes, while remaining simple and familiar. It's my go-to vanilla frosting when time is of the essence, and a far silkier option than anything made with powdered sugar. It's also a great springboard for new flavors, whether you trade toasted sugar for molasses-y Demerara or spike the buttercream with a concentrated fruit purée.

Because it's fully cooked, cakes frosted with Swiss buttercream don't require additional refrigeration; the cake itself will stale faster than the buttercream can spoil. Whether other versions have let you down or you've never made it at all, I hope you'll give my Swiss buttercream a chance. And should the worst come to pass, don't worry: We've got a complete troubleshooting guide that'll put your frosting back on track, no matter the problem.