peanut butter cake with strawberry rhubarb filling

peanut+strawberry+rhubarb

My oldest son loves anything with strawberry rhubarb. So when I came across this flavor combination, I was trying to figure out how I could incorporate peanuts into strawberry rhubarb pie, which is one of his absolute favorite things. I had several different ideas of how I could execute that, but none of them were resonating with me as something I wanted to do in that moment.

Then I reversed my thinking. Instead of strawberry rhubarb being the anchor, what if I made it the highlight? That would put peanut in the spotlight and my brain immediately went to a peanut butter and jelly. But not a sandwich, a peanut butter and jelly in cake form.

After thinking through all the different cakes that I could do, my heart landed on a peanut butter Bundt cake, with layers of strawberry rhubarb filling baked in between.

Spoiler alert – after trying it, my oldest son looked at me and said, “this might be my favorite thing you’ve ever made”.

So why are strawberry and rhubarb such a classic pairing? If you hear the word rhubarb, you almost never hear it without the word strawberry in front of it. I wondered the same thing myself. Does it have to do with the chemistry of the compounds? Is there a specific history behind how these two got started? Is it purely just seasonality? They both come right into ripeness around the same time. Did they start being paired together out of convenience?

Researchers discovered that the answer was actually a combination of all three factors, but the primary driver was the commoditization of cane sugar. Up until the late 18th century, cooks generally considered rhubarb too tart for desserts. People commonly used it in Asia for medicinal purposes. This is the primary reason why rhubarb was brought over to New England. They dried and powdered the roots for use as laxatives and digestive tonics. However, once sugar became more commonplace and easily accessible, cooks found rhubarb stalks much more palatable, making them a great fibrous addition to pie fillings. The fibrous nature of rhubarb stalks provided natural stability for fruit like strawberries, which have a naturally higher water content and could produce watery pies.

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Another fact I learned in my research actually helped explain something I heard as a kid – if you didn’t cook rhubarb correctly, it was TOXIC.

I’m not going to lie, this kept me from even touching rhubarb until I was in my 20s.

Then I figured that it other people didn’t get sick from eating strawberry rhubarb pies, I probably would be ok too. What I learned in this research, is that the actual issue is with the leaves! Early agriculturists tried to treat rhubarb leaves like Swiss Chard or other hearty greens by boiling them. The leaves have high levels of oxalic acid, which can cause severe kidney damage or food poisoning if consumed. So what I was told was actually true but definitely missing context 🙂

There are also chemical compound reasons but not the shared compounds we’ve talked about in other posts. Strawberry and rhubarb actually share very few aromatic compounds but they are both high in acids. Strawberry is high in citric acid and rhubarb contains malic and oxalic acid.

Wait Erica, didn’t you just tell me that oxalic acid is toxic and now it’s ok?

I did! I had to do a deeper dive on that myself to ensure everything I was reading made sense! It’s all about the concentration. In leaves, there’s a 0.5%-1.0% concentration of oxalic acid while there is only 0.05% to 0.19% in the stalks. By cooking the stalks in water or baking them, we further reduce the soluble molecules of oxalic acid.

Anyways, back to the flavors! The citric acid in the strawberries adds a sharp bright sourness while the malic acid is more of the back of the mouth tartness, similar to a tart green apple. The dual acidity of these two fruits truly come to life with the addition of sugar, as they keep the flavors bright and offset all the pure sweet of the sugar. However, using them together without sugar would be a pretty tart mouthful of food.

Let’s add in our last contestant – peanut butter. The higher acidity level in the strawberry rhubarb filling is a perfect offset to the heavy rich texture and flavor of peanut butter. The peanut butter also helps to soften the acidic zing of the filling by coating our tongues with fats, which dulls the acidic hit.

This cake you guys. This cake is both rich and light due to the texture and the brightness of the strawberry rhubarb filling. As it bakes, some jam gets absorbed into the batter around it, creating these nostalgic peanut butter and jelly bites throughout the cake. I mean, look at those beautiful layers!!

The final layer of flavor on this cake features a strawberry rhubarb glaze. I make the glaze by drizzling some of the liquid from the filling on top. Even after it cools, I can strain out about 2 tbsp of liquid from the filling to create the glaze. This spreads the sweet-tart strawberry rhubarb flavor further to balance the richness of the peanut butter.

peanut+strawberry+rhubarb

Now it’s your turn! What would you make with this flavor combination? Tell me in the comments!

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Want other recipes that use peanuts, strawberry or rhubarb? Check out my other recipes below!