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rice krispie treats pressed into a pan

Swiss Meringue Buttercream Filling

4.94 from 47 votes
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Author: EmilyFabulous


  • 1 large egg white, room temp
  • ¼ cup sugar
  • ¼ teaspoon kosher salt
  • ½ cup unsalted butter, room temp and cubed (1 stick)
  • ½ teaspoon vanilla extract
  • ¾ cup powdered confectioner sugar (optional)
  • gel food coloring


  • Make or use a double boiler and whisk sugar and egg white in a heat-safe mixing bowl over a pan of simmering water. Whisk by hand until the sugar has melted and when you rub the mixture between your fingers and you should not feel any granules.
  • Place the egg and sugar mixture into the bowl of a stand mixer and whisk at low speed first, then medium until it's a stiff, shiny ribbon-like consistency. Touch the bottom of the pan to make sure it's cool, then you know it's ready. If it's not cool, your butter will melt and the filling will be runny. Be Patient.
  • Switch to low speed again and add cubes of butter a little at a time making sure it is combined after each addition.
  • Add food coloring and salt and vanilla or almond extract. Increase speed until everything is combined.
  • Add powdered sugar if you would like, I found it added a little more substance and made the butter flavor more subtle.

Any nutrition calculations are only estimates using online calculators. Please verify using your own data.