Tart, Sweet, and a Little Unexpected… The Perfect Spring Cake

As any follower of my blog knows, we eat a lot of cake here at our house. To keep it interesting I am always looking for a seasonal slant on cake. This means I am always keeping my eyes open for any new and or interesting cakes in all of the food blogs and cookbooks I enjoy. So when I stumbled across a post from Saveur “21 cakes for our 20th birthday” I knew I had to check it out. 

As I clicked through the slide show I stumbled across a few gems one of which being Sara Kieffer’s Buttermilk Cake with Rhubarb Buttercream and Cardamom Cream. Whoa! Turns out this cake is not just a mouth full in name but in flavor and deliciousness too but more on that in a moment. When seeing the picture and the recipe I knew I was going to have to give this cake a go. If for no other reason than I have never worked with or eaten rhubarb! Sacrebleu!

One of the many things I love about this cake is that the color is entirely from the rhubarb. Sure you can add a little coloring to it if you need to but if you wait for the reddest of rhubarb to hit your markets you won’t need it.

I did have this cake slated to make earlier in spring but with where we are rhubarb wasn’t available yet. However on my last trip to the market I came across stunning rhubarb and knew now was the time.

Rather than making the buttercream frosting that was in the recipe I use my Italian Buttercream I had in the freezer. If you remember I made a double batch with my Lemon Debutante Cake. I used half for that cake and froze the other half. After letting the frosting thaw I put it back into the mixer with the rhubarb purée and beat it together. I think what I find the most interesting is that when it was cooked down it had a very vegetal taste to it. I was hoping that then it was puréed I would understand the fuss but it still had that odd taste to it. However, when it was added to the buttercream that’s when the magic happened. It turned into this delicious sour flavor. Something you would expect from a sour candy. I finally saw the appeal!


  • 408 grams Cake Flour
  • 1 tablespoon baking powder
  • 1 teaspoon salt
  • 226 grams Unsalted Butter, at room temperature
  • 400 grams Granulated Sugar
  • 4 large eggs, room temperature
  • 2 teaspoons vanilla extract
  • 4 fl ounces Buttermilk
  • 120 grams Sour Cream

Preheat the oven to 350ºF. Grease two 9-inch square pans and line with parchment.

In a small bowl add the flour, baking powder, and salt. Mix together and set aside. In a liquid measure add the buttermilk and sour cream. Mix together and set aside.

In the bowl of a standing mixer fitted with the paddle attachment add the butter and the sugar, beat until light and fluffy, about 3 minutes. Add eggs one at a time, scraping down the sides as needed. Add the vanilla, then beat the batter again at medium speed for 4-5 minutes, until the batter is light and increased in volume.

Using a spatula, fold in the flour and the buttermilk-sour cream mixture in three additions, beginning and ending with the flour.

Divide batter evenly among the prepared cake pans and bake 25-30 minutes, or until set in the center and a cake tester comes out with just the slightest bit of crumb. Run a knife around the edges to ensure it does not stick to the edge as it cools. It will shrink a little and this will help prevent taring.


  • 2 cups (16 ounces) rhubarb, chopped into 1-inch pieces
  • 1/2 cup water

Place the rhubarb and water in a medium sauce pan, bring to a boil, and then let simmer for 15-18 minutes. until rhubarb is tender and most the water has evaporated. Pour the rhubarb into a blender and purée. Pour into an airtight container and allow to fully to cool before using.


Set your stand mixer next to the stove.

  • 400 grams Granulated Sugar
  • 2 ⅝ fl ounces Water

Combine the water and the sugar in a small sauce pan, melting the sugar, and raising to a temperature of 248ºF.


  • 5 ¼ ounces Egg White (about 5 whites depending on the size of your eggs)
  • 1 teaspoon Cream of Tartar

In the bowl of an electric mixer fitted with the whisk attachment add the egg whites and the cream of tartar. Whisk on slow just till the whites are frothy but not whipped. This is to prevent the cream of tartar from getting clumpy. Once the sugar as reached the desired temperature leaving the mixer on a low speed drizzle in the syrup in a constant stream until all the syrup has been added. Raise the speed slow as it builds up volume working towards a high speed. Once at the higher speed let run for 10 minutes to fluff and cool the mixture.

The goal is to get the mixture to 70-75ºF however I was only able to get my mixture to about 80º and it still worked. You don’t want the mixture too warm as it might melt the butter instead of whip it causing the mixture to split. To help cool the mixture you can fill a large ziplock with ice and hold it against the bowl while it’s running for the 10 minutes.

  • 1 ½ pounds Unsalted Butter, at room temperature

Once the mixture has cooled and with the mixer on a medium speed, add the butter one dollop at a time until all the butter is added. Raise the speed to high and beat till strong and fluffy. Add:

  • 2 tablespoons Vanilla

Mix well. At this point it’s ready to use. Once your rhubarb purée is cool. Add to the buttercream and mix to your desired saturation. It can be a neat icing effect if you have it streaky rather than perfectly blended…


  • 8 ounces Cream Cheese, room temperature
  • 4 ounces Unsalted Butter, room temperature
  • 100 grams Granulated Sugar
  • 1 teaspoon Vanilla
  • 2 teaspoons Ground Cardamom

Beat the cream cheese and butter on medium-high speed until light and fluffy. Stop and scrape down the mixture. Return the mixer to medium and gradually add the sugar. Beat until smooth, about 3-4 minutes. Stop, scrape down the mixture again. Then add the vanilla and cardamom, and mix until combined.

Also in her original recipe she called for a Cardamom Cream Filling. She did offer a side note that the flavor isn’t for everyone but that if you like it to go for it. The recipe called for 1 or 2 teaspoons of cardamom but after measuring out the 2 I had only a little left so I added it all. I also made the mistake of using 4 ounces of butter instead of 4 tablespoons (2 ounces). I have a bad habit of mis reading recipes, however, this was yet another instance where it didn’t hurt the recipe at all.

All that’s left is assembly. I went way over the top with my piping. I didn’t want to waste any of the icing and was having fun practicing my piping skills. Rather than icing the top of the cake I split the cardamom cream in half and did two layers of it but again assembly of the cake is all to the preference of the baker.

The cake is a bit on the dry side and a bit dense but it still offered a nice crumb to the buttercream and filling. When I went back to re-read the blog post for this cake I noticed that that cake recipe and the instructions are completely different. I was hoping she might have mentioned why the change but I guess some time I will have to give it a go and see for myself. I love seeing what makes different recipes work.

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