Mousseline Buttercream

READY IN: 30mins
YIELD: 4 1/2 cups




  • In a mixing bowl beat the butter until smooth and creamy and set aside in a cool place.
  • Have all other ingredients at room temperature.
  • Have ready a heatproof pouring container ready for the sugar syrup.
  • In a small heavy saucepan heat 3/4 cup sugar and the 1/4 cup water, stirring constantly, until the sugar dissolves and the mixture is bubbling.
  • Stop stirring and reduce the heat to low.
  • (If using an electric range remove from the heat.) In the bowl of a stand mixer unsing the whisk attachment, beat the egg whites until foamy, add the cream of tartar, and beat until soft peaks form when the beater is raised.
  • Gradually beat in the remaining 1/4 cup sugar until stiff peaks form when the beater is raised slowly.
  • Increase the heat and boil the syrup until the thermometer registers 248'F to 250'F (the firm ball stage).
  • Immediately transfer the syrup to the heatproof container to stop the cooking.
  • Pour a small amount of syrup over the whites with the mixer off.
  • Immediately beat at high speed for 5 seconds.
  • Stop the mixer and add a larger amount of syrup.
  • Beat at high speed for 5 seconds.
  • Continue with the remaining syrup.
  • For the last addition, use a rubber scraper to remove the syrup clinging to the heatproof container.
  • Lower speed to medium and continue beating up to 2 minutes or until the bottom of your mixing bowl feels cool to the touch.
  • If not completely cool, continue beating on lowest speed.
  • Beat in the butter at medium speed 1 tablespoon at a time.
  • At first the mixture will seem thinner but will thicken beautifully by the time all the butter is added.
  • If at any time the mixture looks slightly curdled, increase the speed slightly and beat until smooth before continuing to add more butter.
  • When butter is fully incorporated you may add any of the optional flavorings.
  • Place in an airtight bowl.
  • Rebeat lightly from time to time to maintain silky texture.
  • Buttercream becomes spongy on standing.
  • Will keep 2 days room temperature, 10 days refrigerated, 8 months frozen.
  • Allow to come to room temperature completely before rebeating to restore texture or it will break down irretrievably.