Lemony Swiss Meringue Buttercream


This is the recipe that accompanies the rainbow cake found on Martha Stewart’s website, which I used when making Amelia’s Rainbow Cake!

filling/crumb coat ingredients

  • 9 large egg whites
  • 1 3/4 c. sugar
  • 2 c. (4 sticks) unsalted butter, cut into small pieces, room temperature
  • 2 tsp. pure lemon extract

frosting ingredients.

  • 5 large egg whites
  • 1 c. sugar
  • 1 c. (2 sticks) unsalted butter, cut into small pieces, room temperature
  • 1 tsp. pure lemon extract


  1. Make the filling and crumb coat: Cook egg whites and sugar in a bowl over a small saucepan over medium heat, whisking constantly until sugar is completely dissolved. (I used the mixing bowl over a pot of water – this worked fine – except the bowl never seemed to cool down during the entire time I was making this frosting.)
  2. Transfer to the bowl of an electric mixer fitted with the whisk attachment; mix on high speed until mixture is room temperature and soft peaks have formed. With the mixer on medium-low, add butter, one piece at a time, mixing well after each addition.
  3. Remove whisk attachment and switch to paddle attachment. Increase speed to high and beat until buttercream comes together, about 5 minutes; beat in lemon extract.
  4. Make the frosting: In a clean saucepan and bowl of an electric mixer, repeat process in step 1.

These directions made no sense to me. Why wouldn’t you just make everything all at the same time? Right?

So I diverged from the directions and threw all the ingredients into my mixer at the same time. I should note the ingredients barely fit and for a moment I thought the frosting wasn’t going to turn out. After adding the butter, which was quite fun to chuck in one piece at a time, I should mention, the frosting deflated and became very liquidy. I was afraid I hadn’t cooled the egg white mixture down enough.

I panicked thinking I had just wasted 14 eggs and 6 sticks of butter but even more so that my friend was on her way to help me assemble the cake before she took it home! Finally, after way more than 5 minutes, the buttercream came together. I jumped up and down in my kitchen when I saw it forming into buttercream.

I did not have pure lemon extract so I wasn’t able to use that. Instead I had organic lemon flavoring. I added a bit more lemon flavoring to the recipe than what was called for as I thought it needed a bit more flavor. I’m not sure if you would need to do this when using pure lemon extract or not. But you should always cook/bake to your tastes, not just according to the directions. The frosting was a huge hit. Well, the whole cake was. I would definitely recommend this recipe to anyone who likes lemon flavored dessert.

As an aside – I did not need a crumb coat for this recipe. I just slathered the frosting on real thick and didn’t pick up any rainbow-colored crumbs along the way.

Recipe rating: 


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