Sourdough Rhubarb Cake (With Discard or Not)

Double the tang! This Sourdough Rhubarb Cake recipe is the perfect blend of tangy and sweet, making the most of seasonal, tart rhubarb. Whether you enjoy it with or without the optional streusel topping, this cake is a beautiful way to use up your sourdough discard and add a touch of rustic charm to your baking.

Jump to:

• Sourdough in Cakes: But Why? 
• Equipment
• Ingredients and Substitutes
• Step-By-Step Method
• Fermenting Sourdough Cake Batter Overnight
• How To Serve Rhubarb Sourdough Cake? 
• Storage
• More Sourdough Discard Recipes
• Sourdough Rhubarb Cake (With Discard or Not)

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While staying at my in-laws' place on the sunny south coast of England-a welcome break from the usual rainy summers in North Wales-I found myself with a tan, a happy Golden Retriever Sawyer, and a garden full of rhubarb and plums.

With permission to raid the garden, I couldn't resist diving into rhubarb season (which is incredibly long here in England) and whipped up this great recipe for a rhubarb coffee cake right there. It's one of those rhubarb recipes that perfectly captures the flavours of early summer, making it a delightful treat to enjoy with a cup of tea.

Sourdough in Cakes: But Why? 

Sourdough discard is not to be discarded. While it doesn't have enough leavening power to give your bakes that perfect rise, it still brings plenty to the table. So, why use sourdough to make rhubarb cake?

• It's a great way to reduce food waste!
• The acidity in sourdough starter produces a moist cake with a tender crumb, unlike any regular loaf cake (just try our Sourdough Zucchini Bread or Sourdough Discard Raspberry White Chocolate Loaf Cake, and you will understand!).
• Plus, the sourdough tang beautifully complements the tartness of the rhubarb, creating a delicious treat.
• And here's a bonus-the combination of rhubarb and sourdough discard helps prolong the shelf-life of the cake, thanks to the good bacteria acting as a mild preservative.

Fancy muffins instead? Try our Sourdough Rhubarb Muffins!

Equipment

• A digital kitchen scale to measure ingredients by weight (always more precise than measuring by volume). 
• A couple of mixing bowls
• Electric handheld mixer or a stand mixer fitted with a paddle attachment. 
• 9in (23cm) Springfrom round pan (or a square baking pan that's about 7-8in (20cm) - you can then cut your cake into dessert bars)
• A piece of parchment paper

Ingredients and Substitutes

• unsalted butter: softened.
• brown sugar: light or dark brown sugar will ensure an extra moist sourdough cake. 
• eggs: we used medium eggs.
• sourdough starter: 100% hydration, discard or active. if you're planning to ferment the cake overnight, we recommend using discard. 
• plain flour: also known as all-purpose flour. It can be replaced with self-raising flour, in which case, omit the baking powder.  
• baking powder: not to be confused with baking soda. 
• salt.
• milk: we used whole milk, but any dairy or non-dairy milk will work just fine.  
• fresh rhubarb: cut into small pieces (1cm/1/3 inch pieces).

If you choose to make a Streusel topping for your sourdough rhubarb cake, you will also need extra flour, butter, salt and caster sugar (or white granulated sugar). We also love this streusel topping on our Sourdough Plum Cake!

Find the ingredient quantities, detailed instructions and nutritional information in the recipe card at the bottom of the post. 

A Little Extra Flavour for Your Sweet Treat? Feel free to add flavours. We find that lemon zest from a whole lemon, a teaspoon of vanilla extract or a little almond extract work particularly well. You may also substitute rhubarb for apple (or try our Sourdough Apple Cake instead!)

Step-By-Step Method

• Preheat the oven to 170° C (340°F) Fan. Grease the 9-in springform cake tin with butter, and line the base with a circle of parchment paper.

Streusel Topping

• Make the streusel topping by mixing the flour, salt and white sugar in a medium bowl. Add the soft butter and rub everything to course crumbs. Set the topping aside for later.

Sourdough Rhubarb Cake Batter

• Cream the butter and brown sugar in a large mixing bowl using an electric handheld mixer (or in a stand mixer fitted with a paddle attachment). One at a time, whisk in the eggs. Then add the sourdough starter, and mix on low speed just enough to combine.
• In a separate bowl, mix the flour, baking powder and salt. Add the dry ingredients to the wet ingredients and mix just enough to combine.
• Finally, pour in the milk to loosen, but expect a relatively thick batter that will be able to suspend the pieces of rhubarb without them sinking to the bottom. Furthermore, thicker batter helps absorb some of the water content from rhubarb. 
• Fold in the bits of rhubarb, and scoop the batter into a prepared cake tin and even out the top using a rubber spatula.
• Scatter the streusel topping on top of the batter.

Bake

• Place the cake into the preheated oven for 45-50 minutes. If the topping is browning too quickly, cover the sourdough rhubarb cake with a sheet of aluminum foil.
• Once baked, the top should be golden brown and a wooden toothpick (cake tester) inserted should come out clean (unless you hit a chunk of rhubarb - but there should;t be any dough on it).  
• Take the cake out of the oven and let the cake cool down in its tin to room temperature. Run the knife around the outer edge of the cake and take it out of its tin before slicing it into portions.

Fermenting Sourdough Cake Batter Overnight

Fermenting the cake overnight will make it easier to digest, but if you'd like to do that we highly suggest using unfed sourdough starter in this recipe. Active sourdough starter will make a cake that has very uneven crumb. 

Once you mix the cake batter, scoop it into a prepared cake tin and cover it with cling film (plastic wrap). Place the cake in the fridge for up to 12 hours. The next day, top the rhubarb cake with streusel topping and then bake for 5 minutes longer since the batter will need time to warm up. 

How To Serve Rhubarb Sourdough Cake? 

The perfect way to enjoy your rhubarb sourdough cake? Warm it up for 30 seconds in the microwave, then top it with a scoop of vanilla ice cream or a dollop of sour cream. If you're feeling extra fancy, go for custard or vanilla Greek yogurt.

Whatever you choose, it's all dangerously delicious-good luck having just one slice!

Storage

To keep your sourdough rhubarb cake fresh, store any leftover cake in an airtight container at room temperature for up to three days. If you plan to freeze it, use a freezer-safe container to maintain its texture and flavour. While the cake freezes well, keep in mind that the streusel crumb won't retain its extra crunch once thawed, but it will still be delicious.

More Sourdough Discard Recipes

Want to make more sourdough discard desserts? We don't blame you! Preventing food waste with delicious sourdough muffins, sourdough vanilla cupcakes or vegan sourdough chocolate cake is the best way to feel great about yourself!