High Altitude Rhubarb Layer Cake with Candied Rhubarb Curls

This high altitude rhubarb layer cake has three layers of moist and fluffy vanilla cake, filled with sweet rhubarb curd and rhubarb buttercream. Then the cake is topped with the prettiest, edible candied rhubarb curls! This lovely cake is the perfect celebration of rhubarb season.

And while I paired rhubarb with my best high altitude vanilla cake recipe, it would also be wonderful with a white almond cake, almond poppy seed cake, or coconut cake.

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Why You’ll Love This Cake

Sweet and Tart. Rhubarb is an extremely tart vegetable, but when it’s sweetened with sugar, it’s absolutely delicious. The creamy rhubarb curd filling the cake adds the most wonderful rhubarb flavor, as well as keeps the cake incredibly moist.

So Pretty. I mean, these rhubarb curls are so beautiful! I’ve been waiting to make a rhubarb layer cake until I could get my hands on stalks of fresh rhubarb to make the candied rhubarb curls. I love how elegant and dramatic the curls are. How gorgeous would this cake be as a tiered wedding cake, with rhubarb curls cascading down the cake?

Celebrates Rhubarb Season. Fresh rhubarb is only available for a brief time in the spring, so when you see those ruby red stalks appear at your local farmer’s market around May or June, be sure to grab them before someone else does! While you can make the rhubarb curd with frozen rhubarb, you need fresh rhubarb stalks to make the candied rhubarb curls.

High Altitude Tested. I develop all the recipes on my site for Denver’s altitude of 5,280 feet. If you’re at a lower or higher elevation, please see my FAQs for guidance on adjusting recipes for your altitude.

Homemade Rhubarb Curd

The rhubarb flavor in this rhubarb layer cake comes from the homemade rhubarb curd that’s whipped into the buttercream and sandwiched between the cake layers. Rhubarb curd is silky, smooth and creamy, sweet and a little tart, and just a wonderful texture to use as a cake filling. Similar to lemon curd, rhubarb curd is a custardy mixture of egg yolks, sugar, rhubarb juice, and butter, with a little corn starch to thicken it, and freeze-dried strawberry powder to enhance the color and give it more flavor. Be sure to get the recipe here!

TIP: Instead of the rhubarb curd, you can also use rhubarb jam, both to fill your cake and flavor the buttercream.

Ingredients

Cake

• Sugar. Gives the cake sweetness and moisture.
• Cake Flour. With a lower percentage of protein than all-purpose flour, cake flour makes the lightest, softest white cakes and vanilla cakes. Be sure to measure your flour correctly (by lightly spooning it into the measuring cup and sweeping off the excess), so that you don’t pack too much flour into your measuring cup.
• Baking Powder. Leavens the cake for a light, fluffy texture.
• Salt. I use coarse Kosher salt in all of my cooking and baking, to balance the sweetness and enhance the flavors.
• Eggs + Egg Whites. Eggs give baked goods structure and strength. By using several whole eggs, as well as egg whites, the texture of the cake is light and the color nice and white.
• Buttermilk. Adds acidity and moisture for a very soft, tender cake.
• Butter + Oil. A combination of melted butter and oil adds flavor and moisture.
• Vanilla. Use good-quality vanilla extract for the best flavor.
• Rhubarb Curd. For filling the cake layers.

Buttercream

• Butter. I use unsalted butter in my buttercream, and then add a pinch of salt. The butter gives the buttercream richness, flavor, and its fluffy texture.
• Rhubarb Curd. Gives the buttercream a subtle rhubarb flavor.
• Powdered Sugar. Sweetens and thickens the buttercream.
• Meringue Powder. Adds stability and improves the texture.
• Salt. Balances the sweetness.
• Vanilla. Flavor.

See the recipe card at the end of the post for the full ingredients list and instructions.

Instructions

Cake

• Preheat the oven to 350F and spray the bottoms of three 8-inch cake pans with non-stick spray.
• In a large bowl, sift together the sugar, cake flour, baking powder and salt.  Use a whisk to combine the dry ingredients well.
• In another large bowl, whisk together the eggs, egg whites, buttermilk, melted butter, oil and vanilla extract until smooth.
• Add the dry ingredients to the wet, and whisk until combined and smooth, about 10-15 seconds.  Divide the batter between the cake pans.  Tap a few times against the counter to pop any large air bubbles.
• Bake the cakes for about 21-25 minutes, or until a cake tester or a toothpick comes out clean, and the tops spring back when lightly touched.
• Set the pans on a wire rack, cover them loosely with a clean kitchen towel, and cool completely before frosting.  When ready to frost and assemble the cake, remove the cakes from the pans.

TIP: If making the cakes in advance, let them cool until warm, then turn the cakes out and wrap each layer individually in plastic wrap. Store the wrapped cake layers at room temperature overnight, until you’re ready to frost the cake. Or, freeze the wrapped cakes for up to 3-6 months.

Buttercream

• In the bowl of your stand mixer fitted with the whisk attachment, beat the butter for 1 minute until smooth. Beat in the rhubarb curd.
• With the mixer running on low, add the powdered sugar by spoonfuls, the meringue powder and the salt, mixing until thick and combined. Add the vanilla.
• Increase speed to medium and whip for 4-5 minutes (#6 on a Kitchen Aid mixer), scraping the bowl down several times, until light and fluffy. Turn the speed down to “stir” and mix for 1 minute to get rid of any large air bubbles.

Assembly

• Unwrap the cooled cakes. Use a sharp (non-serrated knife) to split each layer so you have a total of 6 layers.
• Place one cake layer on a cake board or cake pedestal, with the split side facing up. Spread 1/4 cup of rhubarb curd over the cake, not quite to the edges. Place another cake layer on top of the rhubarb filling, with the split side facing down. This way, the open crumb of the split cakes can soak up the rhubarb curd. Now add a layer of buttercream.
• Repeat the above step with more layers of cake, rhubarb curd and buttercream. You should have 6 layers of cake, alternating with 3 layers of rhubarb curd and 3 layers of buttercream.
• Note: The layers should alternate like this from the bottom up: cake, rhubarb curd, cake, buttercream, cake, rhubarb curd, cake, buttercream, cake, rhubarb curd, cake, buttercream.
• Frost the cake all over with a thin crumb coat of buttercream. Refrigerate for 30 minutes to chill the crumb coat, then frost all over with a pretty, swirly coat of buttercream.

How to Make Candied Rhubarb Curls

Make the simple syrup.

• Combine the water and sugar in a medium-sized saucepan. Bring to a boil to dissolve the sugar, then remove from the heat. Let cool for 5 minutes while you prep the rhubarb.

Cut the rhubarb ribbons.

• To cut the rhubarb ribbons, lay a rhubarb stalk down on a cutting board. Using a sharp paring knife, gently wedge the knife in at one end, so that it pierces just the outer skin. Glide the knife away from you down the stalk, so that you slice off a long strip of the outer skin. Work your way around the stalk, slicing off as many strips as you can (Image 1).
• Note: A vegetable peeler does not work well for this project, as it peels off shredded, fibrousy strips that are way too thin. Use a paring knife for strips that are thin enough to be flexible, but not so thin that they fall apart.
• Note: No need to throw out the unused portion of the rhubarb stalks, since you’re only using the outer skin. Just chop up what’s left, place it in a freezer bag, and freeze to use in jam or a pie.

Soak the rhubarb.

• Place the rhubarb ribbons in the simple syrup, and let them soak for 5 minutes (Image 2).

TIP: Don’t throw away the simple syrup after soaking the rhubarb! Save the rhubarb syrup to sweeten lemonade or summer cocktails.

Dry the rhubarb curls in the oven.

• Preheat the oven to 200F, and line a large baking sheet with parchment paper or a nonstick baking mat so the candied rhubarb doesn’t stick.
• Remove the rhubarb ribbons from the simple syrup. For large, loopy curls, arrange the ribbons in big curls (Image 3 & 4). For ringlets, lay the ribbons out flat in a straight line, which you will shape into ringlets after they dry for a bit (Image 5 & 6).
• Dry the candied rhubarb for about 60-90 minutes, until it feels pretty dry.
• Note: If you’re making ringlets, then let the strips dry for about 30 minutes, then wrap the warm rhubarb ribbons around a wooden chopstick, place them back on the baking sheet, and continue to dry in the oven.

Decorate your cake.

• Line a container with a piece of parchment paper or wax paper. Gently transfer the rhubarb curls to the container. When they’re warm from the oven, they can be brittle and break easily if you’re not gentle. Keep them loosely covered for up to 1 day, until you’re ready to decorate your cake.
• Since the candied rhubarb will soften as it sits on the moist cake, I’d suggest waiting to place them on your cake until you’re ready to present the cake.

Rhubarb Simple Syrup

Just look at this lovely pink syrup! After soaking the rhubarb in the simple syrup, even for just five minutes, it turns the loveliest shade of pink with a subtle rhubarb flavor. Pour the syrup into a clean glass bottle or jar and keep refrigerated for up to 3 months. Use the rhubarb syrup to sweeten lemonade or summer cocktails!

Be sure to read all of my BAKING FAQs where I discuss ingredients, substitutions and common questions with cake making, so that you can be successful in your own baking! I also suggest reading these comprehensive posts on making Perfect American Buttercream, How to Stack, Fill, Crumb Coat and Frost Layer Cakes and How to Use Piping Bags.

Frequently Asked Questions

Should I use frozen or fresh rhubarb?

For the rhubarb curd, you can use either fresh or frozen rhubarb. For the candied rhubarb curls, though, you have to have whole, fresh stalks of rhubarb to cut the rhubarb ribbons.

What can I use instead of the rhubarb curd?

If you’re not up for making the rhubarb curd, it’s a bit quicker to make rhubarb jam. Or buy a jar of jam. Jam also makes a perfect cake filling, and works great whipped into the buttercream.

Can I make the cake or rhubarb curls in advance?

Cake. To make the cake in advance, bake and cool the cake, then wrap each layer individually in plastic wrap. Keep at room temperature for up to 1 day before frosting the cake, or freeze the cake layers for 3-6 months.

Buttercream. Buttercream freezes well, too. You can make the buttercream and freeze it in a labeled freezer bag for 3-6 months. Thaw to room temperature before frosting the cake.

Rhubarb Curls. The rhubarb curls won’t keep as long, and you should only make them within 24 hours of decorating your cake. Since the candied rhubarb will soften as it sits on the moist cake, I’d suggest waiting to place them on your cake until you’re ready to present the cake.

Is this a high altitude cake recipe?

Yes, I based my rhubarb layer cake on my high altitude vanilla cake recipe. I recommend reading this article on adjusting recipes for various altitudes, if you’re wanting to bake this cake at low altitude or sea level.

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