This recipe is enough to fill and frost a three-layer 8-inch (20cm) round cake. Creamy, silky, and light buttercream infused with champagne flavor. It is not overly sweet and is sure to make any occasion feel extra special!
In a metal or heatproof bowl, put the egg whites and sugar. Briefly whisk by hand. Place the bowl over a saucepan with water (to create a double boiler) over medium-high heat. Ensure that the bottom of the bowl is not touching the water. Whisk the mixture until it registers 160 F (70 C) on a candy thermometer.
Transfer the egg whites in a stand mixer bowl. Beat with whisk attachment on high speed until medium-stiff peaks, about 8-10 minutes. Switch to paddle attachment and on low speed, add the butter a few at a time, then the vanilla extract.
With the mixer still on low speed, add the champagne (See Note 2) little by little. You may not need all - add according to your liking. Once the champagne is incorporated, turn up the speed to medium-high until buttercream is smooth and silky, about 3-5 minutes.
Notes
(Note 1) You can make the buttercream ahead and store in the fridge for up to 7 days or in the freezer for up to 2 months. On the day you'll be using the buttercream, bring it to room temperature then remix again.
(Note 2) If you’re making your buttercream ahead, add the champagne on the day you’ll be using the buttercream.