Cake Frosting: The Silky Smooth Swiss Meringue Recipe

Instructions:

1. Prepare the Bain-Marie: Fill a medium saucepan with about 1 inch (2.5 cm) of water and bring it to a simmer. Ensure your heatproof mixing bowl sits on top without touching the simmering water.
2. Combine and Heat: Place the egg whites, caster sugar, and salt into the heatproof bowl. Place the bowl over the simmering water.
3. Whisk Constantly: Whisk the mixture continuously by hand until the sugar is completely dissolved. Check by rubbing a small amount between your fingers—it should feel perfectly smooth, not grainy.
4. Check Temperature: Continue heating until the mixture reaches 160°F (71°C). This pasteurizes the egg whites. Remove the bowl immediately from the heat.
5. Transfer and Whip: Pour the warm mixture into the bowl of the stand mixer fitted with the whisk attachment.
6. Whip to Stiff Peaks: Start on medium speed, gradually increasing to high speed. Whip for 8–12 minutes until the mixture forms stiff, glossy peaks (the meringue).
7. Cool Completely: Continue whipping on medium-low speed until the meringue bowl is completely cool to the touch (approx. 70°F / 21°C). This is absolutely critical; if the meringue is warm, the butter will melt.
8. Switch Attachments: Replace the whisk with the paddle attachment. Turn the mixer to low speed.
9. Add Butter Gradually: Add the softened, cubed butter one piece at a time, waiting about 5 seconds between additions.
10. The Curdle Stage (Don’t Panic!): The mixture will look like a curdled, chunky mess at this point—like cottage cheese. This is normal.
11. Whip Through: Increase the speed to medium-high and continue mixing for 3–5 minutes. The mixture will suddenly come together, transforming into a thick, smooth, and glossy buttercream.
12. Flavour and Finish: Add the vanilla extract and mix until just combined. If the frosting is too soft, chill the bowl in the refrigerator for 10–15 minutes, then re-whip until smooth and spreadable.