Cast Iron Rhubarb Upside Down Cake

There’s a particular type of alchemy that happens when sugar and butter are introduced to a hot cast iron pan. I first learned about this as a young child watching my mom throw Myers Dark Rum into a pan with butter, sugar, and bananas before casually lighting it on fire. I was amazed that such magic was possible, but bananas flambé are for a future post. Today, we’re talking rhubarb.

It’s spring, so it’s rhubarb season. Rhubarb blasts into our spring garden at Eden Hill and makes its presence known, its wide leaves confidently spreading across our garden beds. It’s almost hard to harvest it. After so many months of wanting green, I genuinely find it hard to take some away. But then I taste fresh asparagus, I see rhubarb leaves shading out young spinach plants, and I get hungry for cake and pie and rhubarb sauce. As the rhubarb starts to look tempting, the cast iron comes out.

The original version of this recipe, as I know it, was published by the New York Times in 2011. My mom cut it out of the newspaper and tucked it into a cookbook (probably The Best Recipe). From there, it quickly became a classic in our family. At least once a year, we’d hunt down the scrap of paper, eventually scribbled with notes, and rediscover the magic of butter and brown sugar and cast iron and, of course, rhubarb. 

Except the cast iron bit of this reminiscing wasn’t in the original recipe. It was an adaptation — one of those scribbles — we introduced. Perhaps it was because we kept the springform pans the original recipe calls for in the basement and didn’t feel like walking thirty feet. Cast iron pans were closer at hand. Or perhaps it was my mom’s generational knowledge of the magic of cast iron for baking. Whatever the reason, we never went back after trying the result.

As for sourcing rhubarb: If you don’t grow rhubarb, you will be able to find it in many farmer’s markets and grocery stores until mid-summer. I highly recommend planting some in your garden, though, and it doesn’t need to be in a vegetable garden! As a hardy perennial with lots of visual interest, rhubarb is an amazing addition to any landscape — and eating it may turn out to just be a bonus.

And as for picking a cast iron pan: I’ve scaled this pan for a cast iron pan 6-8 inches in diameter. I find that this produces a cake perfect for 6, possible to stretch to serving 8, and ideal for 1 if I want it all for myself. The recipe can easily be doubled, but don’t get too caught up in the details (like having the precise amount of rhubarb). You’re cooking in cast iron — it should be casual.

Cast Iron Rhubarb Upside Down Cake (serves up to 8)

Ingredients

• 1 stick + 2 tbsp butter at room temperature
• 2 cups of chopped rhubarb*
• 1 tsp cornstarch
• 3/4 cup granulated (white) sugar
• 1/4 cup light brown sugar
• 1 cup all-purpose flour
• 3/4 tsp baking powder
• pinch fine sea salt
• zest from one lemon(ish)
• 1/2 tsp vanilla extract
• 2 eggs
• 2 tbsp sour cream or yogurt
• 1 tsp lemon juice

Preparation  

Preheat oven to 350.

Melt 2 tablespoons of butter in the cast iron pan you’ll be baking in. Add brown sugar and stir with a until smoothly combined and a little bubbly. The butter will remain a little separated, and that is ok. Remove from heat and set aside. 

Mix rhubarb, cornstarch, and 1/4 cup granulated sugar in bowl. 

In the bowl of a stand mixer**, cream 1 stick of butter with 1/2 cup sugar and lemon zest with the paddle attachment, until fluffy (about 4 minutes). Add the eggs to the bowl one at a time, mixing between each. Add the sour cream, and the lemon juice. Mix until combined.

With the mixer on low speed, add the flour, baking powder, and salt.

Pour the rhubarb into the cooled cast iron on top of the brown sugar mixture, and distribute evenly. Then pour the batter on top and spread with a spoon.

Bake on the middle rack for between 45 min and an hour, depending on your oven. The top of the cake should be browned and firm to the touch.

Cool the pan for about 5 minutes on a wire rack, or on a cool burner on your stove. Slide a knife around the edge before turning out onto a dish for serving. This must be done while the cake is still warm, or the caramel will harden and stay stuck to the bottom of the pan.***

Serve with a scoop of plain yogurt for breakfast, or ice cream for dessert.

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If you don’t have an appropriately sized cast iron pan you can use a cake pan, but you really need a 9 or 10-inch cast iron pan. It’s a versatile size that is easy to store, and is perfect for everything from making a grilled cheese to baking a cake, as this recipe is evidence of. We find our best cast iron at yard sales and antique stores, and are partial to early 20^th century Griswold and Wagner pieces. These can be pricey if restored, but you can often find ones that just need a good cleaning for a great deal.

There are also apparently some wonderful contemporary makers of true cast iron pans, but we find the older examples are the best bang for your buck.

And if the idea of caring for cast iron has you spooked, it’s really not as complicated as people make it out to be. There’s a whole industry now built on telling you that cast iron needs to be treated like a baby. Surprise, it doesn’t. Use it, wash it with normal dish soap****, and let it dry thoroughly before storing. We keep our most used pan on our stove most of the time so it may be used to fry an egg, cook a sausage for lunch, and then to make fried rice for dinner before being washed. It works for us.

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Some additional notes:

*I like to cut each stalk in half lengthwise and then slice into ¼” pieces.

**Or just use a hand mixer or arm strength. Sometimes all you have is a wooden spoon and a whisk, and that’s ok.

***Sometimes a few pieces of rhubarb will get left behind when you turn the cake over. You’re welcome to add them back on top of the cake, or you can eat them as a ‘tax’ for your efforts.

*****I grew up with a great fear about washing cast iron because it’d ruin the ‘seasoning’. Turns out, the whole thing about not washing it dates back to a time when dish soap was very lye heavy to cut through grease. Lye is very good at breaking down fats, which is part of why we use it in our tallow soaps, but when a soap has a high percentage of lye it can be quite caustic — sort of like a ‘clarifying’ shampoo vs. a moisturizing shampoo. Both get your hair clean, but one might leave you with hair that feels like straw. Using lye heavy soap on cast iron isn’t awesome, so we were all taught not to wash cast iron with soap. Today, that lesson is still remembered but the reason doesn’t apply. Typical liquid dish soaps are not lye heavy (although many do have some amount of lye, often labels ‘sodium hydroxide’), so washing cast iron with a little soap is totally fine. Use a soft sponge, and a stiff bristled brush to spot clean any stubborn bits. Do not put cast iron in the dishwasher. Please.

Served on an original prototype for our Palatine Collection plate in Buttermilk — these plates will be restocked soon. I promise.