Desserts
America's Test Kitchen rhubarb upside down cake delivers the perfect balance of tart rhubarb and ultra-moist cake layers, crowned with a caramelized sugar crust that's crisp yet tender. This recipe transforms humble ingredients into a showstopping dessert that's foolproof for home bakers—no special skills required, just precise technique and patience. The secret lies in pre-cooking the rhubarb to intensify its flavor while keeping it just tender enough to melt into the cake.
What sets this version apart is the moist cake batter, achieved through a combination of buttermilk and sour cream that creates a tender crumb without being dense. The upside-down technique ensures the rhubarb stays juicy while the sugar topping develops that coveted caramelized crown. Every slice reveals layers of flavor: bright rhubarb, buttery cake, and that irresistible crunch from the sugar topping.
This recipe includes troubleshooting tips for common issues like uneven baking or sticking cake, so you'll get perfect results every time. The rhubarb prep is simple—just chop and simmer—but the timing matters to avoid a soggy cake. Once baked, the cake's golden crust will have everyone asking for seconds, while the moist interior stays rich and flavorful.
Perfect for spring gatherings, potlucks, or when you want to impress with a restaurant-quality dessert that's actually easier than it looks. The recipe scales well too, making it ideal for larger crowds. Let's get baking!
Ingredients for america's test kitchen rhubarb upside down cake
Tart rhubarb, ultra-moist cake layers, and a caramelized sugar crown—this is your spring baking game-changer.
| Ingredient | Amount | Notes |
|---|---|---|
| Rhubarb 🍓 | 2 ½ lbs | Fresh, trimmed and chopped |
| Granulated Sugar 🍚 | 2 cups | For rhubarb prep and topping |
| All-Purpose Flour 🌾 | 2 ½ cups | Sifted, plus extra for pan |
| Buttermilk 🥛 | 1 ½ cups | Full-fat for moisture |
| Sour Cream 🥛 | ½ cup | Full-fat for tenderness |
| Large Eggs 🥚 | 2 whole | Room temperature |
| Unsalted Butter 🧈 | 1 cup | Cold, cubed for cake |
| Baking Powder 🍞 | 2 tsp | Aluminum-free preferred |
| Salt 🧂 | ½ tsp | Fine sea salt |
| Vanilla Extract 🌿 | 1 tbsp | Pure vanilla preferred |
| Brown Sugar 🍚 | 1 cup | Packed, for caramelized crust |
| Light Corn Syrup 🍯 | ¼ cup | For glossy caramelization |
| Ground Cinnamon 🌶️ | ½ tsp | Optional for warmth |
Rhubarb is the star here, so pick stalks that are firm and vibrant red. The thicker the stalks, the better the texture—aim for 1-inch pieces after chopping. For the best flavor, use organic rhubarb if possible, and don't skip the pre-cooking step. It intensifies the tartness while keeping it tender. Whole Foods or local farmers markets usually have the freshest stalks in spring. If you're prepping ahead, store chopped rhubarb in the fridge for up to 2 days—it'll keep its bright color longer if you sprinkle it with a little sugar.
Buttermilk and sour cream are non-negotiable for that ultra-moist crumb—full-fat versions only. No buttermilk? Mix 1.5 cups milk + 1.5 tbsp vinegar, let sit 5 minutes. For the sugar topping, brown sugar is a must—it caramelizes beautifully. Light corn syrup adds that glossy finish we all love. Swapping in maple syrup at half the amount works in a pinch, but it'll be less crisp. The cake batter needs to be just thick enough to hold its shape—if it's too runny, add 1 tbsp more flour. And trust me, room-temperature eggs make all the difference in a tender crumb.
This cake is best served the day it's baked—the crust gets even better overnight. Store leftovers at room temperature in an airtight container for 3 days, or freeze slices wrapped in plastic for up to 1 month. To reheat, pop slices in a 350°F oven for 5-7 minutes—just enough to warm the filling without drying out the cake. The rhubarb filling keeps its juicy goodness when reheated this way. And if you're making this for a crowd, bake two pans at once—they disappear faster than you can say 'seconds, please!'
Why You'll Love This Recipe
- No-Fuss Layers: I swear by this upside-down method—just chop rhubarb, dump it in the pan, and let the sugar caramelize while you mix the batter. The cake stays moist, the rhubarb stays tender, and I’m not babysitting a single step.
- Tart-Sweet Magic: That rhubarb and sugar combo? It’s like a grown-up fruit compote hugging a buttery cake. The sour cream in the batter keeps it rich but light, and the buttermilk gives it that subtle tang that makes every bite feel special.
- Weekend or Weeknight: Slice it for breakfast with coffee, pack it for lunch, or serve it at brunch with a dollop of whipped cream. Honestly, I’ve even reheated leftovers in the microwave—it’s that good, and the rhubarb stays jammy, not mushy.
- Budget Bright Spot: Rhubarb is cheap in season, and this recipe stretches a little cake far with generous fruit layers. Plus, the sour cream and buttermilk make it feel indulgent without breaking the bank—my wallet thanks me every time.
Step-by-step instructions for america's test kitchen rhubarb upside down cake
This upside down cake delivers a perfect balance of tart rhubarb and ultra-moist cake layers—here's how to nail it.
Prepare the Rhubarb Filling and Caramel Topping
Preheat your oven to 350°F and grease a 9-inch round cake pan generously with butter. In a large bowl, combine the 2.5 lbs rhubarb with 1 cup granulated sugar and 0.25 cup light corn syrup. Stir gently to coat the rhubarb evenly—this ensures sweetness penetrates while preserving its natural tartness.
Transfer the rhubarb mixture to the prepared pan and spread it into an even layer. In a small saucepan over medium heat, melt together 1 cup brown sugar and 1 cup unsalted butter until smooth. Pour this caramel mixture over the rhubarb, pressing down lightly to help it set. Sprinkle with 0.5 tsp ground cinnamon if using, then bake for 20 minutes until the rhubarb softens and the caramel starts to set slightly.
Mix the Cake Batter for Perfect Texture
While the rhubarb bakes, whisk together the 2.5 cups all-purpose flour, 2 tsp baking powder, and 0.5 tsp salt in a medium bowl. In a separate large bowl, combine the 1.5 cups buttermilk, 0.5 cup sour cream, and 2 whole large eggs. Whisk until smooth—this creates a tender base for the cake.
In a separate bowl, beat the 1 cup unsalted butter (cold and cubed) with 1 cup granulated sugar on medium speed until light and fluffy—about 3-4 minutes. Add the 1 tbsp vanilla extract and mix for another 30 seconds. Gradually add the dry ingredients to the butter mixture, alternating with the buttermilk mixture, beginning and ending with the dry ingredients. Mix just until combined—overmixing develops gluten and makes the cake tough.
Bake the Cake to Golden Perfection
Remove the rhubarb filling from the oven and spread the cake batter evenly over the top, creating a smooth surface. Return the pan to the oven and bake for 35-40 minutes or until a toothpick inserted into the center comes out clean. The cake should be golden brown and spring back gently when pressed.
Here's the key: as soon as the cake is done, carefully invert it onto a wire rack or plate. Let it cool completely before slicing—this ensures the rhubarb filling stays intact and the caramel crown holds its shape. The contrast of warm, spiced rhubarb and moist cake layers makes every bite unforgettable.
Serve with Confidence
Once fully cooled, slice the cake into 8 equal servings using a sharp knife. The rhubarb filling should be tender but still hold its shape, topped with a glossy caramel crown that cracks slightly when cut. Serve at room temperature with a dusting of powdered sugar or a dollop of whipped cream to complement the tart-sweet balance.
This cake keeps well for up to 3 days at room temperature, wrapped tightly in plastic. For best results, store the rhubarb filling separately and assemble just before serving to maintain texture. The secret to this recipe is patience—letting the rhubarb soften properly and the cake cool completely ensures that first bite is always perfect.
Pro Tips For Making America'S Test Kitchen Rhubarb Upside Down Cake
- STEAM THE RHUBARB FIRST: Don’t skip this step—raw rhubarb is tough and releases too much liquid when baked. Simmer 3 cups chopped rhubarb with ½ cup sugar for 8–10 minutes until it breaks down into a jammy consistency. This keeps the cake moist and prevents a soggy bottom later.
- WEIGH YOUR FLOUR: Scooping flour from the bag packs too much volume, and this cake relies on precise ratios. Use a kitchen scale for the 2 cups all-purpose flour—it should measure 240 grams. Trust me, the texture stays lighter when you do.
- DON’T OVERMIX THE BATTER: The second you add the buttermilk and sour cream, stop mixing after just 10–12 strokes. Overworking the batter introduces too much gluten, and this cake needs to stay tender. A few lumps? Doesn’t matter—it’ll disappear when baked.
- CHILL THE BATTER 10 MINUTES: Pour the batter into the prepared pan, then pop it in the fridge for 10 minutes before baking. This lets the flour absorb the liquid evenly, so the cake rises straight instead of doming or cracking. (Yes, even if you’re impatient like me.)
Essential equipment for america's test kitchen rhubarb upside down cake
Cake Pan Essentials
You'll need a 9-inch round cake pan with sides at least 2 inches tall—I recommend a nonstick pan like Wilton's Perfect Results for easy release. If your pan isn't nonstick, grease it thoroughly with butter and dust with flour to prevent sticking. Avoid dark-colored pans—they can over-bake the edges. For extra insurance, I line the bottom with parchment paper, cutting it to fit snugly before adding the rhubarb. 🧁
Mixing Tools
A stand mixer with the paddle attachment makes mixing the cake batter effortless, but a hand mixer works too. For the dry ingredients, use a medium-sized bowl and a whisk to sift the flour and baking powder together. I swear by a fine-mesh sieve to avoid lumps in the batter. A spatula helps scrape down the sides when mixing—don't skip this step, or you'll miss flavorful batter at the bottom. 🥄
Measuring Precision
This recipe demands accurate measurements, so invest in a stainless steel measuring cups set like OXO Good Grips. For the granulated sugar and brown sugar, pack the brown sugar firmly into the cup—don't scoop it directly from the bag. Use a bench scraper to level off dry ingredients like flour. A digital kitchen scale is ideal for butter and sugar, but if you're measuring by volume, use the spoon-and-level method for consistency. 📏
Baking Gear
An oven thermometer is a game-changer—your oven's temperature can be off by 25°F or more, and this cake needs precise heat control. I use a Thermoworks Oven Thermometer to ensure my oven hits 350°F accurately. For cooling, a wire cooling rack is essential to prevent sogginess. If you don't have one, a baking sheet lined with parchment works in a pinch. 🔥
Optional Extras
For the caramel topping, a small saucepan with medium heat control is perfect for melting the sugar and butter smoothly. If you're adding ground cinnamon, use a fine-mesh strainer to dust it evenly over the rhubarb. A sharp serrated knife (like Mercer Culinary Genesis) makes slicing clean, even layers without crushing the cake. Trust me, the difference is noticeable! ✨
Nutrition facts
Frequently asked questions
Why does the rhubarb need to be pre-cooked in this recipe?
Pre-cooking the rhubarb intensifies its natural tartness while keeping it tender enough to blend perfectly with the cake layers. This step prevents a watery filling that could make the cake soggy. The 20-minute bake time with sugar and corn syrup also helps develop a glossy finish and subtle caramel notes that complement the cake's sweetness.
Can I substitute strawberries for rhubarb in this recipe?
While strawberries would change the flavor profile, you can use them—but expect a sweeter, fruitier dessert. For best results, reduce the sugar in the rhubarb mixture by 0.5 cup since strawberries are naturally sweeter. Also, pre-cook strawberries for only 10-12 minutes to avoid mushiness, as they break down faster than rhubarb.
How do I prevent the cake from sticking to the pan?
Grease your 9-inch round pan generously with butter, then dust with flour or use a nonstick spray. For extra insurance, line the bottom with parchment paper cut to fit snugly. The key is patience when inverting—let the cake cool completely in the pan for 10 minutes before carefully flipping it onto a wire rack. A sharp knife tapped around the edges helps release stubborn spots.
Is this cake gluten-free or vegan-friendly?
This recipe isn't naturally gluten-free or vegan, but you can adapt it! For gluten-free, use a 1:1 flour blend and add 0.5 tsp xanthan gum to the dry ingredients. For vegan, replace the eggs with 2 flax eggs (2 tbsp ground flax + 6 tbsp water) and use vegan butter and buttermilk alternatives. Note: texture may vary slightly, and the caramel topping will need vegan butter.
Can I make this cake ahead of time?
Yes! Assemble the cake up to 24 hours ahead and store it at room temperature in an airtight container. For longer storage, freeze the cake (without frosting) for up to 1 month. Thaw overnight in the fridge, then let it sit at room temperature for 1 hour before serving. The rhubarb filling stays juicy when properly stored—just avoid slicing too soon after baking.