Swiss meringue buttercream

Step by step

• Whisk egg whites and sugar in a bowl over simmering water until the sugar dissolves and the mixture reaches 160°F (71°C)
• Whip to stiff, glossy peaks and keep whipping until the bowl feels cool
• Add soft but cool butter a piece at a time
• Whip until smooth and silky, then add vanilla and salt

Rescue it

• Soupy: chill the bowl 10–15 minutes, then whip again
• Curdled or lumpy: warm the outside of the bowl briefly and whip
• Keep whipping; it nearly always comes together

Watch for

A completely grease-free bowl helps the whites whip to full volume.