Delicious Lunar Rhubarb Cake Recipe with Lemon

This Lunar Rhubarb Cake is the perfect summer cake, with tart rhubarb perfectly balanced by sugar and zesty lemon, all topped with a buttery streusel. The name of this cake comes from its unique appearance. The surface resembles the moon’s craters, created by the fruit and brown sugar sinking into the top. The incredible aroma while it bakes is simply irresistible, filling your home with a comforting, sweet fragrance. Enjoy it for breakfast, as a snack, or save it for dessert and serve with ice cream – this rhubarb cake is the perfect summer treat.

This rhubarb cake recipe holds a special place in my heart. My grandmother made it every summer when her garden was overflowing with rhubarb. For years, I believed it was her secret recipe until I discovered my husband’s grandmother also made a similar cake. Turns out, Lunar Rhubarb Cake has been a staple in Canadian kitchens for decades, long before the internet and Pinterest made sharing recipes easy. It’s one of those beloved cakes everyone seems to remember, but no one knows where it came from. We’ve updated the traditional recipe by adding lemon to brighten the flavors even more. It still has all the great flavor of the homemade rhubarb cake I remember, but with a zesty lemony twist. 

If you are looking for another traditional cake recipe try our chocolate wacky cake recipe, this old fashioned chocolate cake is made without dairy but is still delicious.

Ingredients (and substitutes)

• Butter: Adds richness and ensures a tender crumb. It is important to use room temperature butter for best results.  For a dairy-free option, substitute with margarine or a plant-based butter alternative.
• Sugar: This recipe calls for white sugar in the cake batter and brown sugar in the strusel topping.  Brown sugar will give the topping a beautiful color and caramel flavor that pairs beautifully with the tart  flavor of the rhubarb. 
• Vanilla Extract: Infuses a lovely depth of flavor. If possible always use pure vanilla extra for the best flavor. 
• Eggs: Essential for binding the ingredients and giving the cake its structure. I use large eggs for this recipe.
• Lemon:  for this recipe I zest and juice a whole lemon to get the best flavor possible. In a pinch, you could use just bottled lemon juice.  
• Lemon Juice: Adds a bright, zesty flavor. If lemons aren’t available, lime juice or a splash of white wine vinegar will work as alternatives. If you don’t have lemon, orange zest and juice can provide a different citrusy note.
• Flour: Forms the base of the cake, giving it structure. I use All Purpose Flour. You can use whole wheat flour for a heartier texture, or opt for a gluten-free flour blend if you’re avoiding gluten.
• Baking Soda: Helps the cake rise and become light and fluffy. If you only have baking powder, you can use 3 times the amount as a substitute.
• Milk: Adds moisture and richness. Homogenized milk is our go-to, but 2% regular milk will also work perfectly fine. 
• Rhubarb: known for its tartness and vibrant pink color, brings a unique blend of sweet and sour flavors to the cake. Rhubarb season runs from early spring through summer, making it widely available in grocery stores and farmers’ markets during this time.  For this recipe, both fresh and frozen rhubarb stalks work well, rhubarb should be roughly chopped into 1 inch pieces. 
• Cinnamon: Adds a warm, comforting spice to the topping. If you want to mix things up, try using pumpkin pie spice or nutmeg for a different flavor profile.

How to make homemade rhubarb cake

Preheat: Grease a 9×9 inch cake pan with butter and preheat your oven to 350℉.

Cream Butter: In a large bowl, beat the room temperature butter and sugar together until light and fluffy, using a fork or electric mixer.

Mix: Add the eggs, vanilla extract, lemon juice, and lemon zest to the butter and sugar mixture. Mix until fully combined, then pour in the milk and mix again until smooth.  Stir in the dry ingredients into the wet ingredients and mix until the batter is thick and smooth.

Add Rhubarb: chop rhubarb into one inch pieces and toss chopped in 1 tbsp flour, then fold 1.5 cups into the batter. Reserve .5 cups of rhubarb.

Prepare Brown Sugar Topping: Mix the butter, cinnamon, and brown sugar with your hands until the mixture is smooth and crumbly.

Bake: spoon batter into the prepared pan. Sprinkle the brown sugar topping in large chunks over the batter, then add the remaining ½ cup of rhubarb. Bake for 1 hour and 10 minutes to 1 hour and 20 minutes, or until a toothpick inserted into the center comes out clean. Allow to cool for a few minutes before serving

Questions about making lunar rhubarb cake:

Can I use frozen rhubarb?

​Yes, you can use frozen rhubarb. Ensure that the frozen rhubarb is chopped to the correct size and is dusted in a tbsp of flour to ensure that any moisture is absorbed. Using frozen rhubarb may increase the baking time slightly. 

What can I substitute for the rhubarb in this cake?

If you are not a rhubarb lover or you just aren’t able to find any rhubarb at your local store.  You can substitute almost any fruit in this rhubarb coffee cake, just be sure to toss it in flour.  Apples, blueberries and plums would likely be a delicious compliment with the flavors in this cake.  Green apples would probably be the closest match for the tartness of the rhubarb. 

How do I store lunar rhubarb cake?

Store the cake in an airtight container at room temperature for up to 3 days or refrigerate for up to a week. This cake is best eaten fresh the day it is made as the buttery brown sugar topping will be form an extra delicious crusty layer that will soften when it is stored.   

Lunar Rhubarb Cake with Lemon

Lunar Rhubarb Cake with Lemon is a delightful summer dessert featuring tart rhubarb balanced with sweet sugar and zesty lemon, all topped with a buttery streusel. Its unique, crater-like surface and irresistible aroma make it perfect for breakfast, snacking, or dessert. This versatile cake, rich in family tradition, can be made with either fresh or frozen rhubarb and simple ingredients

5 from 1 vote

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Prep Time 10 minutes mins

Cook Time 1 hour hr 10 minutes mins

Total Time 1 hour hr 20 minutes mins

Course Dessert

Cuisine Canadian

Servings 12

Equipment

• 1 9×9 baking pan

Ingredients

  

Rhubarb Cake

• ½ cup butter room temperature
• 1 ¼ cups sugar
• 1 tsp vanilla
• 2 eggs large
• 2 tbsp lemon juice freshly squeeze is best
• zest whole lemon
• 2 cups all purpose flour
• 1 tsp baking soda
• ¼ tsp salt
• ⅔ cup milk whole milk preferred
• 2 cups rhubarb roughly chopped
• 1 tbsp flour

Brown Sugar Topping

• ¼ cup butter
• 2 tsp cinnamon
• ½ cup brown sugar

Instructions

 

• Preheat: lightly but thoroughly grease a 9×9 baking pan with butter. Preheat oven to 350℉
• Cream Butter: add room temperature butter and sugar to a large bowl. Cream together either using a fork or electric stand mixer.
• Mix: add eggs, vanilla, lemon juice and zest and continue to mix until fully combined. Add milk and mix one final time.
• Add Dry Ingredients: add flour, baking soda, and salt. Mix together until fully combined. Batter should be relatively thick.
• Add Rhubarb: toss rhubarb in 1 tbsp of flour. Fold 1.5 cups of rhubarb into the cake batter using a spoon. (see note)
• Prepare Brown Sugar Topping: using your hands mix together topping ingredients until smooth.
• Bake: scrape the batter into the prepared baking pan. Sprinkle the brown sugar topping over the batter, it should be in larger chunks. This will create the moon like craters on the top. Finally, sprinkle on the remaining ½ cup of rhubarb. Bake in the oven for 1 hour and 10 minutes to 1 hour and 20 minutes. Cake is done when an inserted tooth pick comes out clean.

Notes

Note – it is important to toss the rhubarb in flour to prevent it from sinking to the bottom of the cake batter during baking.  Don’t skip this step.

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