This simple rhubarb chocolate cake is filled with intense dark chocolate flavor and dotted with tart pieces of rhubarb.
It takes just a couple of minutes to prepare the batter and it is easy to stir together by hand. No mixer is needed.
Looking for more rhubarb recipes? Try this rhubarb creme brulee.
Why You Will Love This Recipe
- The tartness of the rhubarb pairs perfectly with sweet moist chocolate cake.
- Adding rhubarb to your cake adds moistness and is a great excuse to have a second slice. Rhubarb is a vegetable after all.
- Because this cake is baked in a loaf pan it is smaller making it a great dessert for a smaller family. No endless leftovers or waiting for a party to make this cake.
Rhubarb is typically a less common vegetable due to its short growing season which means you might be unfamiliar with it.
What is Rhubarb?
Rhubarb is a tart vegetable that looks like pink celery. I remember my mom always made a rhubarb custard pie every spring but for some reason, I never tried it.
One of my favorite parts of cooking is trying new recipes and experimenting with new ingredients and techniques. This spring I decided to tackle rhubarb. Rhubarb is typically in season from late March until early June.
Note: Rhubarb leaves are toxic and should not be consumed. They contain oxalic acid which can build up in your body and lead to kidney failure.
Rhubarb is classified as a vegetable, but it is often used as a fruit. The leaf stalks can be eaten raw, they have a crisp texture similar to celery. Rhubarb is commonly cooked with sugar and used in pies, crumbles, and other desserts. Rhubarb has a strong, tart taste.
Buying, Storing, and Preparing Rhubarb
Look for rhubarb stalks that are flat and firm. Avoid rhubarb stalks that are limp and curled.
Refrigerate unwashed rhubarb stalks in a plastic bag for up to 3 days.
There is no need to peel the stalks just pull off any obvious strings and trim off any rough areas. Next, cut the stalks into ½ to 1-inch pieces against the grain of the stalk to help break up the stringiness. Rhubarb has a high amount of acid. It is best to cook rhubarb in non-reactive cookware.
Bittersweet Baking Chocolate: Use freshly chopped baking chocolate and not chocolate chips, which won't melt as smoothly.
Dutch-Process Cocoa Powder: Dutch-process cocoa powder is much darker than regular cocoa powder. This is my favorite Duch-process cocoa powder.
Hot Coffee: Adding hot liquid to the batter blooms the cocoa powder and intensifies the flavor. The addition of coffee to any chocolate dessert also increased the chocolate flavor.
You can also mix ½ a cup of boiling water with 1 teaspoon of instant espresso powder.
Salt: I add at least a pinch of salt to all of my recipes. Salt complements and intensifies the other flavors. For all of my recipes, I use Morton Kosher Salt which packs more densely than Diamond Crystal Kosher Salt. If you are using Diamond Crystal Kosher Salt you will want to double the amount of salt you add.
Baking Soda: The baking soda reacts with the acid in the chocolate, brown sugar, and buttermilk to raise the cupcakes.
Buttermilk: Make your own buttermilk by adding ½ a tablespoon of lemon juice or white vinegar to ½ a cup of milk. Let the mixture sit for 10 minutes until it begins to curdle.
Vegetable Oil: Oil helps to keep the cupcakes moist. You could also substitute other neutral-flavored oils like canola oil.
Egg Yolk: Cold eggs are easier to separate than warm eggs. Separate your eggs and then return the egg whites to the refrigerator to use for another purpose. Let the egg yolks set out on the counter to warm to room temperature.
Vanilla Extract: My preference is to use pure vanilla extract rather than imitation vanilla. I usually make my own vanilla extract by soaking vanilla beans in vodka.
Rhubarb: Rhubarb has a short growing season and can be difficult to find. You may need to substitute frozen rhubarb for fresh rhubarb.
If using frozen rhubarb allow it to thaw and drain thoroughly before adding it to the cake batter.
See the recipe card for quantities.
Kitchen scale: Kitchen scales make baking faster and neater. Accuracy matters in baking. Scales are more precise than measuring cups. Too much flour or not enough sugar can dramatically change a recipe. The most accurate way to bake is to measure your ingredients by weight rather than volume.
A kitchen scale also reduces the number of dishes you will need to wash because you are measuring each ingredient directly from the container into the mixing bowl without the use of measuring cups.
This scale from OXO is the one I use after it was recommended by Alton Brown. What makes this scale great is the display pulls out to make viewing measurements easier when using a large bowl.
Rubber spatula: For folding batters together, I prefer a stiffer spatula like this one from OXO. It fits comfortably in my hand, is dishwasher safe, and is heat-resistant up to 600 degrees Fahrenheit. Both the handle and head are silicone coated which makes it easy to clean and safe to use with my non-stick cookware and bakeware.
Loaf pan: These are my favorite loaf pans. They are heavy duty which means they won't warp and they distribute heat evenly. Plus they are non-stick which makes removing loaves of bread really easy. I hand wash mine to keep them looking their best. Don't worry the non-stick coating also makes clean-up a breeze.
Cooling rack: Cooling racks are essential for cooling baked goods quickly and preventing soggy bottoms. I really like these cooling racks from the Checkered Chef. They are recommended by Cook's Illustrated, are very sturdy, and are free from coatings which means they are safe to use in the oven as well.
In a medium heatproof bowl add the chopped chocolate, hot coffee, and cocoa powder. Let sit for five minutes and then whisk until smooth.
Preheat the oven to 350°F and grease a 9x5 inch loaf pan with baking spray. You can also line the pan with parchment paper to make removing the baked cake easier.
Combine the flour, baking soda, and salt in a medium-sized bowl and set aside.
Whisk the sugars, buttermilk, oil, egg yolks, vanilla extract, and chocolate mixture together in a large bowl.
Stir in the flour mixture until smooth, being careful not to overmix.
Finally, add the chopped rhubarb. Stir until it is evenly distributed.
Pour the batter into the prepared loaf pan.
Bake for 60 to 70 minutes until a toothpick inserted into the center comes out clean.
Cool in the pan on a wire rack for 10 minutes. Then carefully remove the cake from the pan and let it continue to cool on the wire rack.
While this wouldn't be a rhubarb chocolate cake without the rhubarb, feel free to substitute all or some of the rhubarb with equal amounts of berries or shredded and drained zucchini.
Top with a scoop of vanilla ice cream, whipped cream, and/or fresh berries before serving, or serve with a cup of coffee and some fruit to have dessert for breakfast.
Up the rhubarb flavor by topping it with a quick rhubarb compote. In a saucepan combine half a pound of chopped rhubarb with half a cup of granulated white sugar.
Cook over medium heat until the rhubarb has broken down and formed a sauce. Remove from the heat and add a splash of vanilla extract.
Once the cake has cooled, store it in an airtight container at room temperature. This cake should stay moist for up to 3 days.
For longer storage, the cake can be refrigerated for up to 7 days.
- Use room temperature ingredients. Room temperature ingredients are easier to incorporate together.
- Baking times for all recipes are only suggestions. The actual baking time will vary depending upon your oven. It is helpful to know your oven and worth purchasing an inexpensive oven thermometer. Oven temperatures can vary as much as 50 degrees plus or minus.
- Do not overmix the batter. Overmixing can incorporate too much air causing the cake to rise quickly and then fall in the center as it bakes. Overmixing can also create tough cupcakes.
- Allow the cake to cool completely before slicing.
Frequently Asked Questions
Yes! Once it has cooled wrap the cake in a layer of plastic wrap and then either wrap with foil or place the cake in a zip-lock bag. Label with the date and contents and place in the freezer.
This cake can be frozen for up to 3 months. Thaw at room temperature.
The cake is done once a toothpick inserted into the center comes out clean. The cake will also feel firm to the touch, bouncing back when you poke it with your finger.
Probably the most reliable way to check is by using an instant-read thermometer. This one from ThermoWorks is my favorite.
Once the center of the cake has reached 200 - 205 degrees Fahrenheit it is done.
More Springtime Desserts
Simple Rhubarb Chocolate Cake
- mixing bowl
- loaf pan
- 4 ounces bittersweet baking chocolate finely chopped
- ½ cup hot coffee
- ⅔ cup Dutch-process cocoa powder
- 1 ¼ cup all-purpose flour
- ¾ teaspoon baking powder
- ½ teaspoon kosher salt
- ¼ teaspoon baking soda
- ½ cup granulated sugar
- ½ cup brown sugar
- ½ cup buttermilk room temperature
- ½ cup vegetable oil
- 3 egg yolks room temperature
- 2 teaspoons vanilla extract
- 1 ½ cups rhubarb cut into ¼-inch pieces
- In a medium heatproof bowl add the 4 ounces bittersweet baking chocolate, ½ cup hot coffee, and ⅔ cup Dutch-process cocoa powder. Let sit for five minutes and then whisk until smooth.
- Preheat the oven to 350°F and grease a 9x5 inch loaf pan with baking spray. You can also line the pan with parchment paper to make removing the baked cake easier.
- Combine the 1 ¼ cup all-purpose flour, ¾ teaspoon baking powder, ½ teaspoon kosher salt, and ¼ teaspoon baking soda in a medium-sized bowl and set aside.
- Whisk the ½ cup granulated sugar, ½ cup brown sugar, ½ cup buttermilk, ½ cup vegetable oil, 3 egg yolks, 2 teaspoons vanilla extract, and chocolate mixture together in a large bowl.
- Stir in the flour mixture until smooth, being careful not to overmix.
- Finally, add the 1 ½ cups rhubarb. Stir until it is evenly distributed.
- Pour the batter into the prepared loaf pan.
- Bake for 60 to 70 minutes until a toothpick inserted into the center comes out clean.
- Cool in the pan on a wire rack for 10 minutes. Then carefully remove the cake from the pan and let it continue to cool on the wire rack.
Thanks for Reading!
If you try this recipe, let me know! Leave a comment and rate it below! You can also snap a picture and post it on Facebook or Instagram be sure to tag me @RaspberriesandKohlrabi.