Rhubarb Dump Cake

There’s something so comforting about a dessert that feels homemade without the fuss—and that’s exactly what this Rhubarb Dump Cake delivers. It’s the kind of recipe that doesn’t require any fancy ingredients, complicated techniques, or a long prep time. In fact, if you can open a cake mix and pour melted butter, you’re already halfway there!

Dump cakes have been a favorite in our house for as long as I can remember. My mom always had one baking in the oven whenever guests came over or when we needed a quick dessert for a potluck. I remember peeking through the oven door as the cake bubbled and browned, the smell of sugar and fruit filling the kitchen. This version, with its tart rhubarb and golden cake topping, brings all of that nostalgia flooding back with every bite.

Whether you’re working with fresh rhubarb from the garden or a stash from your freezer, this cake is a must-try for late spring through summer. The beauty of it lies in its simplicity: tart rhubarb softened beneath a sweet layer of golden cake that forms right in the oven—no bowls, no mixers, no stress.

So, let’s get to the delicious details!

this recipe

Ingredients You’ll Need:

• 4 cups chopped fresh or frozen rhubarb

• 1 cup granulated sugar

• 1 box (15.25 oz) yellow or white cake mix

• 1 cup water

• 1/2 cup unsalted butter, melted

Tip: If you’re using frozen rhubarb, no need to thaw it first! Just toss it straight into the baking dish.

STEPS: How to Make Rhubarb Dump Cake

Step 1: Preheat and Prep Your Pan

Start by preheating your oven to 350°F. Grease a 9×13-inch baking dish with a bit of butter or non-stick spray to ensure easy cleanup later.

Step 2: Add the Rhubarb

Take your chopped rhubarb and spread it evenly across the bottom of your greased baking dish. Don’t worry if some pieces overlap a bit—that’s totally fine. You want a nice, even base of fruit to start the magic.

Step 3: Sprinkle with Sugar

Next, pour your 1 cup of granulated sugar evenly over the rhubarb. This helps to sweeten the naturally tart flavor and draws out the fruit’s juices as it bakes.

Step 4: Add the Cake Mix

Now for the easiest part—open up your box of yellow (or white) cake mix and sprinkle it directly over the fruit and sugar. No mixing, no sifting, just a simple, even layer over the top. Make sure the entire surface is covered with the dry mix.

Step 5: Pour Water and Butter

Drizzle the 1 cup of water evenly over the cake mix. Again, don’t stir. Then follow with your melted butter, pouring it slowly over the top. You’ll see the butter start to soak into the cake mix—this is what gives you that irresistible, golden-brown crust.

Why You’ll Love This Recipe

This Rhubarb Dump Cake is a fantastic last-minute dessert option. Whether you’re hosting a backyard BBQ, attending a church gathering, or just craving something sweet on a weeknight, this cake has you covered. It comes together in just 10 minutes of prep and bakes into a sweet-tart, gooey-bottomed treat with a buttery top that’s crisp in all the right places.

If you’re someone who loves rhubarb (or even if you’re just starting to explore it), this is a great beginner recipe. It highlights rhubarb’s signature tanginess while balancing it with sweetness and texture. And yes—it pairs beautifully with vanilla ice cream or a big spoonful of whipped cream.

Finish Baking and Serve Your Perfect Rhubarb Dump Cake

Now that your Rhubarb Dump Cake is prepped and ready to bake, the rest is easy. This dessert practically takes care of itself in the oven. It’s one of those “set it and forget it” recipes—except you won’t be forgetting it for long, because the aroma wafting through your kitchen is going to have everyone asking what’s baking.

The beauty of this dump cake is how the ingredients naturally layer and transform during baking. The rhubarb softens and releases its juices, the sugar melts and blends into the fruit, and the dry cake mix absorbs moisture from the water and butter to form a golden, slightly crisp crust on top. There’s no stirring or fussing—just layers of flavor doing their thing while you relax.

Let’s finish this up and get ready to serve!

STEPS: Bake and Serve the Cake

Step 6: Bake to Perfection

Place the prepared baking dish on the center rack of your preheated oven. Bake at 350°F for 45 to 50 minutes, or until the top is a beautiful golden brown and you can see the fruit bubbling up around the edges. The exact time can vary slightly depending on your oven, so check at the 45-minute mark.

You’ll know it’s done when:

• The top is lightly crisp and golden

• The edges are bubbling

• The center no longer looks powdery or dry

Step 7: Cool Slightly Before Serving

Once it’s out of the oven, allow the cake to cool for at least 10–15 minutes before serving. This helps the filling set up just a little and makes it easier to scoop. Trust me—it’s worth the wait.

Tips for the Best Rhubarb Dump Cake

Even though this recipe is incredibly simple, here are a few tips to make sure it turns out perfectly every time:

• Don’t stir: Seriously—resist the urge to mix anything. The magic of a dump cake is in the layering.

• Spread ingredients evenly: While you don’t mix, you do want to make sure the rhubarb, sugar, and cake mix are spread as evenly as possible to ensure even baking.

• Butter distribution matters: Try to drizzle your melted butter across the top as evenly as possible. If you end up with a few dry patches of cake mix after baking, just dot a little extra butter on and pop it back in the oven for a few minutes.

• Use frozen rhubarb straight from the freezer: Don’t thaw it—it releases too much liquid. Frozen rhubarb works perfectly when used straight from the bag.

• Add a flavor twist: Want to shake things up? Toss in a cup of chopped strawberries with the rhubarb for a classic strawberry-rhubarb combo. You could even sprinkle a little cinnamon or nutmeg over the fruit before adding the cake mix.

Serving Suggestions

This cake is best served warm, right out of the oven (after that short cooling period). The combination of the gooey, tart rhubarb layer with the crisp, sweet cake topping is absolutely dreamy.

Here are a few of my favorite ways to serve it:

• With a scoop of vanilla ice cream – The contrast of warm cake and cold ice cream is chef’s kiss.

• Topped with whipped cream – Light and airy, it’s a perfect match for the rich, buttery crust.

• Drizzle of heavy cream or custard – If you’re feeling a little extra, this gives the dish a cozy, old-fashioned vibe.

Make-Ahead and Storage Tips

Rhubarb Dump Cake is great right out of the oven, but it also stores surprisingly well if you have leftovers.

• Refrigerator: Store leftovers covered in the fridge for up to 3 days.

• Reheat: Warm individual servings in the microwave for about 30–45 seconds, or place the whole pan in a low oven (around 300°F) until heated through.

• Freezing: You can freeze it, but note that the texture of the cake topping may become a little softer after thawing. If freezing, wrap tightly and use within 1 month.