If you've ever run a finger along a cake and wondered how it got that glass-smooth finish, this is almost always the answer. Less sweet than American buttercream, and it takes to a smoothing scraper like nothing else.
Swiss meringue buttercream has a reputation for being intimidating, but the technique is really just three checkpoints: dissolve the sugar, cool the meringue completely, and add the butter slowly. Miss any one of those and it'll still probably work out — it's more forgiving than people expect.
The one step people rush (and shouldn't)
The most common issue is adding the butter before the meringue has fully cooled. If the bowl still feels even slightly warm, the butter will melt on contact and you'll end up with soup instead of frosting. Touch the bottom of the mixing bowl before you add a single cube — it should feel completely room temperature, not just "not hot."
If it curdles: this is normal, not a failure. Somewhere in the middle of adding the butter, Swiss meringue buttercream almost always looks broken and lumpy for a minute or two. Keep the mixer running on medium speed and it will come back together into a silky frosting — this is chemistry catching up, not a sign to start over.
Set up a double boiler — a heatproof bowl over simmering water, not touching it.
Whisk egg whites and sugar together gently while warming, just to prevent cooking on the bottom.
Heat to 160°F / 71°C, until the sugar is fully dissolved (test between your fingers — no graininess).
Move to a stand mixer with the whisk attachment. Whip on medium 8–10 minutes until completely cool.
Once cool with stiff peaks, add vanilla and salt.
Add the cubed butter a little at a time. It will look curdled — keep beating until silky.
Notes: Ivory in color, less sweet than American buttercream, and exceptionally smooth — this is the one to reach for when the finish needs to look flawless. Refrigerate up to a week; bring to room temperature and re-whip before using.
by Alejandro, PastryPath · Updated July 2026
