Rhubarb Custard Bars Recipe

There’s something magical about discovering an old-fashioned dessert that feels like it’s been passed down through generations—something your grandmother might have made, quietly cooling on the windowsill on a spring afternoon.

Rhubarb custard bars are exactly that kind of recipe.

I created this version after stumbling across a hand-written note tucked inside an heirloom cookbook. It was labeled “church bake sale favorite.” The moment I made it, I understood why. Tangy rhubarb, nestled into a silky custard base, layered over a buttery shortbread crust, all finished with a dusting of powdered sugar—it’s both humble and elegant.

If you’re looking for a dessert that celebrates rhubarb’s bright tartness without being overly fussy, this is the one.

Keep reading—you’re going to want this recipe in your spring baking rotation.

Why I Love This Recipe

Rhubarb custard bars are special because they strike a rare balance of flavors and textures.

You get the creamy richness of custard paired with the sharp, citrus-like tartness of fresh rhubarb. These two elements alone would be lovely, but what really sets this dessert apart is the crisp shortbread crust anchoring everything underneath. It adds structure, contrast, and a touch of buttery saltiness that brings the whole thing together.

This is the type of dessert people don’t expect to love until they’ve had a bite. Then they ask for seconds—and the recipe.

It’s also incredibly versatile. You can serve it at a backyard gathering or cut into elegant squares for an afternoon tea spread. It’s bright, nostalgic, and homey all at once.

Plus, it’s a brilliant way to use rhubarb during peak season when gardens and markets are bursting with the stuff.

There’s no need for whipped cream or glaze—just a simple dusting of powdered sugar. That simplicity makes the rhubarb shine and the custard luxuriously smooth.

This is comfort baking at its finest: reliable, rewarding, and designed to be shared.

Ingredients for Rhubarb Custard Bars

To make these bars, you’ll need three separate components: the shortbread crust, the custard filling, and the rhubarb.

Each layer has a distinct role and together, they form a beautifully structured dessert.

For the shortbread crust:

You’ll need basic pantry staples—nothing fancy, but quality matters here. Butter should be unsalted and cold for a flaky finish. All-purpose flour creates structure, while powdered sugar adds a fine sweetness and tenderness.

Ingredients:

• Unsalted butter – cold and cubed
• All-purpose flour
• Powdered sugar
• A pinch of salt

For the custard filling:

This is where richness and tang meet. The eggs create a smooth, firm custard while the flour helps it set. Sugar balances rhubarb’s tartness without overwhelming it. A splash of vanilla adds warmth.

Ingredients:

• Large eggs
• Granulated sugar
• All-purpose flour
• Vanilla extract
• A touch of cream or milk (optional, for added richness)

For the rhubarb:

Fresh rhubarb is key. Look for stalks that are deep red and firm. Avoid any that are limp or overly fibrous.

Ingredients:

• Fresh rhubarb, chopped into small ½-inch pieces
• Lemon zest (optional, enhances tartness)

Finishing:

• Powdered sugar, for dusting (optional but lovely)

This isn’t a recipe where you need hard-to-find items, but using the best ingredients you can find will elevate the final flavor dramatically.

How Much Time Will You Need?

From start to finish, you should plan for about 1 hour and 20 minutes, most of which is hands-off baking and cooling time.

Here’s how it breaks down:

• Prep Time: 20 minutes
• Bake Time: 40–45 minutes
• Cooling Time: 20–30 minutes before cutting

For best results, don’t rush the cooling. The bars slice cleanest and hold their shape once they’ve had time to set fully.

If you’re serving these for a gathering, they can even be made a day ahead—just keep them refrigerated and slice just before serving.

How to Make These Rhubarb Custard Bars

Let’s walk through the process in clear steps so you know exactly what to do at each stage.

Step 1: Prepare the pan and preheat the oven

Start by preheating your oven to 350°F (175°C).

Grease a 9×13-inch baking pan and line it with parchment paper, leaving some overhang on the sides to help lift the bars out later.

This helps prevent sticking and ensures a clean release after cooling.

Step 2: Make the shortbread crust

In a mixing bowl, combine flour, powdered sugar, and salt. Add in the cold, cubed butter.

Use a pastry cutter, two forks, or your fingertips to work the butter into the flour until the mixture resembles coarse crumbs.

Press this mixture firmly into the bottom of the prepared pan. You want an even, tight layer without gaps.

Bake for 15 minutes, or until the edges start to turn pale golden.

Remove from the oven and let it cool slightly while you prepare the filling.

Step 3: Make the custard

In a large bowl, whisk the eggs until smooth and pale.

Add sugar, flour, and vanilla extract, and whisk until well combined. If using cream, stir it in now.

The mixture should be glossy and pourable—not too runny.

Step 4: Add the rhubarb

Stir the chopped rhubarb into the custard mixture until evenly distributed.

If using lemon zest, fold it in at this point for a slight citrus lift.

Step 5: Assemble and bake

Pour the rhubarb custard mixture evenly over the warm crust.

Gently smooth the top with a spatula.

Return the pan to the oven and bake for 35–40 minutes, or until the custard is set and no longer jiggles in the center. The top may look lightly golden in places.

Step 6: Cool and slice

Let the bars cool completely in the pan.

Once cool, lift them out using the parchment overhang and place on a cutting board.

Dust with powdered sugar before slicing into squares or bars.

Refrigerate leftovers, if there are any.

Substitutions

This recipe is forgiving and flexible—ideal for small tweaks if needed.

Butter substitute:
If you prefer, you can use plant-based butter for a vegetarian or lactose-free version of the crust. Make sure it’s a firm block butter and not spreadable.

Rhubarb substitute:
While rhubarb is the star, you could mix in strawberries or raspberries if your rhubarb supply is small. Just keep the total fruit volume the same.

Gluten-free option:
Use a 1:1 gluten-free flour blend in place of the all-purpose flour in both the crust and custard. Choose a blend with xanthan gum for best texture.

Milk or cream:
The cream in the custard is optional, but adds a luxurious mouthfeel. You can omit it entirely or use a dairy-free cream alternative like coconut cream.

Egg substitute:
For an egg-free version, use a custard-style vegan alternative with cornstarch or silken tofu, though the texture may be slightly different.

Small changes won’t compromise the taste—but stick to the basic ratios to maintain the custard structure.

Best Side Dishes for Rhubarb Custard Bars

Pairing rhubarb custard bars with the right accompaniments can turn a simple dessert into a more complete experience. Here are three ideas to consider:

1. Lemon Lavender Tea
The floral and citrus notes of this tea perfectly complement the tartness of rhubarb without overpowering it. Serve warm or iced.

2. Fresh Berry Salad with Mint
A chilled berry medley with strawberries, blueberries, and a sprinkle of mint adds brightness and freshness to balance the creamy custard.

3. Vanilla Bean Ice Cream
A scoop of smooth vanilla ice cream adds cool contrast and a touch of indulgence. Let it melt just slightly over a warm bar.

Serving and Presentation Tips

Presentation can transform these humble bars into an elegant dessert for guests—or simply make them feel more special on your table.

Here are a few thoughtful serving ideas:

• Chill before slicing: These bars cut best when fully cooled. For cleaner edges, refrigerate for 30 minutes before slicing with a sharp knife. Wipe the blade between cuts.
• Dust just before serving: A light dusting of powdered sugar adds a beautiful visual contrast and a delicate sweetness. Wait until just before serving to keep it from dissolving into the custard.
• Serve on white or neutral-toned platters: The rosy flecks of rhubarb pop visually against a pale background. Add a small garnish—like a mint leaf or lemon twist—if you’re plating individually.
• Pair with tea or coffee service: These bars are perfectly portioned and pair naturally with hot drinks, making them a charming addition to afternoon tea spreads.

They’re beautiful, simple, and speak for themselves. No frosting, glaze, or embellishment needed.

Tips and Tricks to Make This Recipe Even Better

Want to get bakery-style results at home? Here are a few pro tips to take your bars to the next level:

• Use cold butter for the crust: This ensures that the shortbread base stays flaky and crumbly. Warm butter results in a greasy, dense base.
• Chop rhubarb small and evenly: Uneven chunks can cause uneven baking and texture. ½-inch pieces allow the fruit to soften just right in the custard without becoming mushy.
• Bake in the lower third of the oven: This encourages a golden crust while preventing the top from browning too quickly.
• Let them cool completely before cutting: It can be tempting to slice early, but warm custard doesn’t hold shape well. Cooling is crucial for perfect bars.
• Line the pan with parchment: Not only does this prevent sticking, it also makes removal and slicing much easier.

These small habits make a big difference—and once you’ve nailed them, this recipe becomes nearly foolproof.

Common Mistakes to Avoid

Even a simple recipe like this has a few areas where things can go wrong. Here’s what to watch out for:

• Overmixing the crust: You want to press the crust firmly into the pan, but don’t knead or overwork it. Overmixed dough becomes tough instead of tender.
• Undercooking the custard: If the center is still jiggling after baking, give it a few extra minutes. The custard should be set, with no visible liquid in the center.
• Using watery rhubarb: Very young or overripe rhubarb can release a lot of liquid. If your rhubarb seems extra juicy, pat it dry after chopping.
• Cutting too soon: Wait until the bars are fully cool. Slicing while warm results in messy edges and a runny texture.
• Skipping the parchment: It might seem optional, but without it, the crust can stick—especially if your pan isn’t non-stick.

Avoiding these pitfalls will help guarantee a polished, bakery-style finish every time.

How to Store It

Rhubarb custard bars store very well, making them an ideal make-ahead dessert.

Short-Term Storage:

• Store in an airtight container in the refrigerator for up to 4 days.
• Place parchment or wax paper between layers if stacking to prevent sticking.

Freezing Instructions:

• Freeze individual bars on a baking sheet until solid.
• Transfer to a freezer-safe bag or container, separating layers with parchment.
• Freeze for up to 2 months.

To serve from frozen, thaw in the refrigerator overnight and dust with powdered sugar before serving.

Avoid leaving them out at room temperature for more than a few hours, especially in warmer months—the custard needs to stay cool to hold its shape and texture.

FAQ

Q1: Can I use frozen rhubarb for this recipe?
Yes. If using frozen rhubarb, thaw completely and drain off excess moisture. Pat it dry to avoid watering down the custard.

Q2: Is this recipe very tart?
The rhubarb provides tartness, but the custard balances it with sweetness. If you prefer sweeter desserts, you can increase the sugar slightly or pair with sweet sides like ice cream.

Q3: Can I make this recipe gluten-free?
Absolutely. Use a 1:1 gluten-free flour blend that contains xanthan gum. It works well in both the crust and the custard without sacrificing texture.

Q4: What can I substitute for rhubarb?
Try chopped strawberries, raspberries, or even cranberries (sweetened). Just keep total fruit volume the same.

Q5: How far in advance can I make these?
They can be made up to two days ahead and kept refrigerated. Wait to dust with powdered sugar until just before serving.

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