Easy Rhubarb Custard Cake Recipe Ready in 70 Minutes

Rhubarb season is honestly one of my favorite times of year, and this easy rhubarb custard cake recipe is the first thing I make when those tart pink stalks show up. I threw it together on a chaotic Tuesday night last spring, and my kids were absolutely floored by it. Here’s the thing that gets everyone: you don’t do anything fancy. A box of yellow cake mix handles the base. You pile on the rhubarb, sugar, and heavy cream, then just slide it in the oven. The cream sinks down all on its own and forms this gorgeous, creamy custard layer underneath. It’s like magic, I promise.

Table of Contents

Table of Contents

Why You Will Love This Easy Rhubarb Custard Cake Recipe

Seriously, where do I even start? This cake checks every box for me. Here’s why it keeps showing up in my kitchen:

• Prep takes just 10 minutes. That’s it.
• You only need one box of cake mix and a handful of simple ingredients you can grab at any grocery store.
• No fancy techniques, no special equipment. Beginner bakers, this one’s for you.
• The tangy rhubarb cuts through the sweet custard perfectly. It never feels too rich or too sugary.
• One 9×13 pan feeds 12 people, so it’s perfect for potlucks or family dinners.
• Busy weeknight? No problem. The oven does almost all the work.

Easy Rhubarb Custard Cake Recipe Ingredients

Good news: the ingredient list here is wonderfully short. Here’s everything you need to pull this together:

• 1 box yellow cake mix, plus the water, eggs, and vegetable oil listed on the box. The exact amounts depend on your specific brand, so just follow those package directions.
• 4 cups chopped rhubarb, cut into roughly half-inch pieces. Fresh is great, but thawed frozen rhubarb works too. If you go the frozen route, make sure you thaw it completely and drain off all that extra liquid before measuring.
• 1 and one-quarter cups granulated sugar
• 1 and one-half cups heavy cream
• Whipped cream or Cool Whip for serving, totally optional but honestly highly recommended

That’s really it. Nothing obscure, nothing hard to find.

Ingredient Notes and Substitutions for Easy Rhubarb Custard Cake Recipe

Let me break down what each ingredient is actually doing here, because it helps to understand why you can’t just swap things out randomly.

The yellow cake mix is your easy, reliable base. A white cake mix works fine as a swap if that’s what you have on hand.

Heavy cream is the star of the whole custard trick. It’s heavy for a reason. Lower-fat options like half-and-half or regular milk will not sink and set the same way. Don’t try to lighten it up here or you’ll lose that creamy layer completely.

The granulated sugar sweetens the tart rhubarb as everything bakes together. If your rhubarb is on the milder side, you can pull back the sugar by a few tablespoons.

Frozen rhubarb is totally fine, but drain it really well first. Extra liquid will mess with the texture of the finished cake.

How to Make Easy Rhubarb Custard Cake Recipe

This is genuinely one of the easiest things I make all year. Follow these steps in order and you’re golden.

1. Preheat your oven to 350 degrees F. Give it time to fully heat up before the pan goes in.
2. Prepare your yellow cake mix batter according to the package directions, using whatever water, eggs, and vegetable oil your specific box calls for. Mix it up just like normal.
3. Pour the batter into a well-greased 9×13 inch baking pan and spread it out evenly.
4. Scatter all 4 cups of chopped rhubarb evenly over the top of the batter. Don’t press it in. Just lay it right on top.
5. Sprinkle the 1 and one-quarter cups of granulated sugar evenly over the rhubarb layer.
6. Pour the 1 and one-half cups of heavy cream slowly and evenly over everything.
7. Now stop. Do not stir. I know it looks a little strange just sitting there in layers, but that’s exactly the point. The layering is what creates the custard. The moment you stir it, you lose the whole effect.
8. Slide the pan into the oven and bake at 350 degrees F for 60 to 70 minutes. You’re looking for a deep golden brown top and a center that doesn’t jiggle when you gently shake the pan.
9. Let it cool for just a few minutes, then serve it warm with a big dollop of whipped cream or Cool Whip on top.

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Tips for the Best Easy Rhubarb Custard Cake Recipe

• Do not stir after adding the rhubarb, sugar, and cream. Seriously. Those separate layers are what sink down and form the custard. Stirring breaks the whole magic of this recipe.
• The cake is done when the top is golden brown and the center feels set. Give the pan a gentle little shake. No jiggle means it’s ready.
• Don’t panic if your toothpick comes out a little moist. The custard layer is naturally creamy, so a perfectly clean toothpick isn’t always the goal here. Look for the golden top and the set center instead.
• Grease your pan really well. The custard layer can stick if you’re not generous with it.
• This cake is wonderful warm, but it’s also really good cold straight from the refrigerator the next day. The custard firms up a bit and the flavors deepen overnight.

Easy Rhubarb Custard Cake Recipe Variations

Once you’ve made this once, you’ll start thinking about all the ways you can play with it. Here are a few of my favorites that still keep that custard layer intact.

• Toss in a cup of fresh strawberries alongside the rhubarb. Strawberry rhubarb is such a classic combo, and it works beautifully here. If you love strawberry rhubarb, you might also enjoy our strawberry rhubarb pie recipe.
• Swap the yellow cake mix for a spice cake mix. It adds this warm, cozy flavor that feels perfect in the fall.
• Dust a little cinnamon right over the sugar layer before the cream goes on. Just a light sprinkle makes a real difference.
• A white cake mix works as a straight swap for yellow if that’s what’s in your pantry.

Just remember, whatever you change, don’t touch that no-stir rule.

Serving Suggestions for Easy Rhubarb Custard Cake Recipe

My favorite way to serve this is warm, straight from the pan, with a big spoonful of Cool Whip or freshly whipped cream on top. The cold cream against the warm custard is just so good.

A scoop of vanilla ice cream works really well too. It melts right into the cake and makes everything even more dreamy.

This cake is also perfect for potlucks. One 9×13 pan cuts into 12 generous slices, so it travels well and feeds a crowd without any fuss.

Storage and Reheating for Easy Rhubarb Custard Cake Recipe

Leftovers keep really well in the refrigerator. Just cover the pan tightly or transfer slices to an airtight container and they’ll stay good for up to 4 days.

Honestly, cold slices straight from the fridge are amazing. The custard layer firms up overnight and the flavors get even better. My kids actually prefer it that way the next morning.

If you want it warm, pop a single slice in the microwave for about 20 to 30 seconds. That’s all it needs.

I’d skip the freezer on this one. The custard layer doesn’t hold up well after freezing and thawing, and the texture gets a little sad. Just enjoy it fresh within those 4 days.

Nutritional Information

Here’s a rough breakdown per slice, based on the recipe cutting into 12 servings. Keep in mind these are estimates and your actual numbers will vary depending on the cake mix brand and other ingredients you use.

• Calories: 380
• Fat: 18g
• Saturated Fat: 8g
• Unsaturated Fat: 9g
• Trans Fat: 0g
• Cholesterol: 65mg
• Sodium: 310mg
• Carbohydrates: 52g
• Fiber: 1g
• Sugar: 38g
• Protein: 4g

Frequently Asked Questions About Easy Rhubarb Custard Cake Recipe

Can you use frozen rhubarb in this easy rhubarb custard cake recipe?
Yes, absolutely. Frozen rhubarb works great in this rhubarb dessert. Just make sure you thaw it completely and drain off all the extra liquid before you measure out your 4 cups. Too much extra moisture will mess with the custard layer.

Why does the cream sink to the bottom?
It’s just simple kitchen science. The heavy cream is denser than the cake batter, so it naturally sinks down through the rhubarb and sugar as everything bakes. That’s what creates the custard cake layer. It happens on its own every single time, as long as you don’t stir.

How do you know when the cake is done?
Look for a deep golden brown top and a center that doesn’t jiggle when you gently shake the pan. Don’t stress if your toothpick comes out a little moist. The custard layer is supposed to be creamy.

Can you make this easy rhubarb custard cake recipe ahead of time?
You can. It keeps covered in the refrigerator for up to 4 days, and honestly the flavors get even better overnight. Just reheat slices in the microwave for 20 to 30 seconds if you want it warm.

Can you use a different cake mix flavor?
Yes. White cake mix is a straightforward swap for the yellow cake mix rhubarb base. A spice cake mix also works really well if you want a warmer, cozier flavor.

Share Your Easy Rhubarb Custard Cake Recipe Results

I really hope you give this one a try. When you do, come back and leave a comment or drop a star rating below. It genuinely makes my day to hear how it turned out for you. And if you snap a photo, please share it on social media and tag Frosty Recipes. I love seeing your kitchens and your families enjoying this cake as much as mine does. You can also share your results with our community on Facebook.

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