Rhubarb Custard Bars Recipe

There’s something about rhubarb season that always pulls me into the kitchen, even if I swore I was taking a day off. These rhubarb custard bars are a beautiful celebration of contrast—sweet meets tart, creamy meets crisp, soft meets crumbly.

I first made a version of these bars during a quiet afternoon at work. We were between dinner rushes, and someone had brought in rhubarb from their garden. While everyone else went back to prepping creme brûlées and mousses, I took that rhubarb and built something I hadn’t made in years: a buttery shortbread base, a soft, sweet custard, and sharp little slices of pink rhubarb right on top. 

I didn’t expect it to be a hit, but they vanished faster than the tiramisu. That’s when I knew I had something worth perfecting.

I’ve since tweaked that recipe into something I make every year without fail. These bars are nostalgic, comforting, and just the right kind of indulgent.

Why You’ll Love These Rhubarb Custard Bars

✔️These bars have it all: creamy custard, buttery base, tart rhubarb, and a golden crumble top that brings the whole thing together. 

✔️They’re easy to slice, even easier to devour, and they keep beautifully in the fridge.

✔️The contrast between the sharpness of rhubarb and the rich, vanilla-scented custard is what makes these stand out. 

✔️Every bite is soft yet structured—perfect with a cup of tea or as a cool, refreshing dessert on warmer days.

Ingredients You’ll Need

These rhubarb bars use simple, classic ingredients, but each one plays a key role in getting that perfect balance of flavour and texture.

For the Shortbread Base & Crumble

• All-Purpose Flour – The foundation of your base and crumble. It holds everything together while keeping that signature shortbread bite. You can use plain flour in the UK and Australia—just make sure it’s not self-raising.
  Sugar – Adds just enough sweetness to contrast the tart rhubarb. I prefer caster sugar here for its fine texture, but granulated works too.
• Cold Unsalted Butter – The magic behind that crumbly, melt-in-your-mouth texture. Make sure it’s cold—straight from the fridge cold. If you’re baking in a hot climate, chill the bowl too.
• Baking Powder – Just a touch gives the shortbread a subtle lift, so it’s not too dense.
• Salt – Always. Even in sweet recipes, it sharpens flavour and rounds out the sweetness. I like fine sea salt for even distribution.

For the Custard Layer

• Egg Yolks – Rich and velvety, they give the custard its golden colour and luxurious texture. Room temperature yolks whisk more smoothly—worth remembering if you’re short on time.
• Sugar – Sweetens the custard and helps it set as it bakes. If you like a slightly deeper flavour, try replacing a spoonful with light brown sugar.
• Cornstarch – This thickens the custard in the oven without needing to cook it on the stove. Sift it in to avoid any lumps.
• Whole Milk & Heavy Cream – The combo keeps the custard creamy and rich without being heavy. You can swap cream for double cream in the UK, or thickened cream in Australia.
• Vanilla Extract – Don’t skip this. It brings warmth and balance to the whole bar. Use a good-quality extract or vanilla paste for a stronger, more aromatic flavour.

For the Rhubarb

• Fresh Rhubarb, Thinly Sliced – The star of the show. Look for firm, vibrant stalks. Thin slices bake more evenly and nestle into the custard perfectly. No need to pre-cook—it softens as it bakes.
• Sugar – Just a little, to tame the tartness without muting the rhubarb’s natural zing. If you’ve got very mature rhubarb, you might want to toss it in sugar and let it sit for 10 minutes first.

How to Make Rhubarb Custard Bars

This bake comes together in three parts: a quick shortbread dough, a whisk-together custard, and thinly sliced rhubarb. No blind baking or water baths here—just layer and bake.

Step-by-Step Instructions

1. Preheat your oven to 175°C (350°F) and line a 23cm (9-inch) square pan with parchment.
2. Make the shortbread base: Combine flour, sugar, baking powder, and salt in a bowl. Rub in the cold butter with your fingertips until it forms a crumbly dough. I sometimes use a food processor if I’m in a rush.
3. Press two-thirds of the mixture firmly into the pan and bake for 12–15 minutes until lightly golden. This gives the base time to set.
4. Whisk the custard: No need to cook it! Just whisk together the yolks, sugar, and cornstarch until smooth, then add the milk, cream, and vanilla. It should be silky and pourable.
5. Assemble: Pour the custard over the hot base. Top with sliced rhubarb.
6. Crumble the remaining dough over the top and bake for 35–40 minutes. It should jiggle slightly in the center but be set around the edges.
7. Cool completely and refrigerate for at least 2 hours (or overnight). Dust with icing sugar before serving.

Flavour & Texture: What to Expect

These bars are a dreamy contrast. The base is rich and buttery, like a good shortbread should be, while the custard stays smooth and just-set, never rubbery. The rhubarb softens into ribbons, bringing bursts of tartness that keep each bite balanced.

I always say this is the kind of dessert that whispers spring—light, cool, and deeply comforting.

Ingredient Substitutions & Variations

Depending on where you live, a few swaps might help:

• In the UK or Europe: If you can’t find heavy cream, double cream works too—just reduce it slightly since it’s richer.
• Australia: Use thickened cream for the custard layer and plain flour in place of all-purpose.
• Gluten-Free Option: Swap the flour with a gluten-free blend that includes xanthan gum.
• No Rhubarb? Try chopped strawberries or raspberries—tart fruits work best here.
• Add a citrus twist: A little lemon zest in the custard pairs beautifully with rhubarb.

Pro Tips for Perfect Bars

• Cold butter only. This helps create the perfect crumb in both the base and topping.
• Don’t overbake. The custard should still wobble slightly in the centre—carryover heat will finish the job.
• Strain the custard. Pour the liquid through a fine mesh strainer into the base to ensure it’s perfectly smooth.
• Use thin rhubarb slices. They cook faster and nestle into the custard more evenly.
• Chill overnight. These bars slice much more cleanly once they’ve had time to set properly.

I’ve made this recipe dozens of times during bakery shifts, for spring markets, and even once for a wedding dessert table. It always disappears.

Rhubarb Tips & Tricks

If you’re new to rhubarb, don’t worry—it’s much easier to work with than it looks. And once you know a few basics, you’ll want to use it in everything.

First things first: never eat the leaves. They contain oxalic acid and are toxic—so always trim them off and discard them. Use only the stalks, which range in color from pale green to deep red. 

Color doesn’t affect flavor much, but bright red stalks do look extra pretty in these bars.

To prep rhubarb, I trim both ends and slice it into thin pieces—about ½ cm thick (¼ inch). This helps it cook evenly and soften just enough while baking in the custard. I sometimes toss mine in a little sugar and let it sit for 10 minutes if the stalks are particularly sharp.

Pro tip: If your rhubarb is really tart, a pinch of ground ginger or cardamom in the custard can add warmth and mellow things out without masking its character. I’ve done this for catering gigs when I wasn’t sure how “rhubarb ready” the crowd would be, and it always goes down a treat.

Perfect Pairings for Rhubarb Custard Bars

These bars are easy to dress up or down depending on the occasion. Here are some pairing ideas I love:

• Tea Time: A light floral tea like Earl Grey, chamomile, or even a rhubarb and hibiscus blend makes a gorgeous combo. I particularly enjoy it with this Starbucks London Fog Tea Latte!
• Coffee Break: A flat white or cappuccino contrasts beautifully with the tart custard and buttery base.
• Brunch Vibes: Serve chilled bars with a scoop of vanilla yogurt and a drizzle of rhubarb compote for a fancy spring brunch.
• Cocktail Hour: Try my Rhubarb French 75 Cocktail, Rhubarb Mojito, or Rhubarb Margarita. Yum!

These bars are the kind of dessert that works just as well on a picnic blanket as it does on a white china plate.

What to Do With Leftover Rhubarb

Bought a big bunch? Here are a few ideas for using up the rest of your rhubarb:

• Make a Quick Compote: Simmer rhubarb with sugar, orange zest, and a splash of water until soft. Serve over porridge, pancakes, or yogurt.
• Freeze It: Rhubarb freezes brilliantly. Chop and freeze raw pieces flat on a tray, then transfer to a bag. No need to thaw before using in future bakes.
• Rhubarb Syrup for Cocktails: Simmer equal parts rhubarb, sugar, and water until soft. Strain and cool. Add to prosecco, lemonade, or gin for a spring-inspired twist.
• Bake Another Treat: Rhubarb crumble muffins, rhubarb upside-down cake, or even a rhubarb and custard tart (if you’re really feeling fancy).

I often grab extra rhubarb when it’s in season because it’s so easy to work into other recipes. The bars might be the main event—but rhubarb’s always got an encore performance in my kitchen.

Bonus Twist: Add a Spiced Almond Crumble

Want to level things up? Replace the reserved shortbread topping with this spiced almond version for a little extra crunch and flavour:

• 2 tbsp ground almonds (or almond flour)
• ¼ tsp cinnamon
• ¼ tsp ground ginger
• 1 tbsp brown sugar
• Mix with your remaining shortbread crumble before sprinkling on top

I made this version for a market stall last year and nearly sold out before lunchtime. It adds warmth and complexity to balance the tang of the rhubarb—and it smells incredible as it bakes.

Make-Ahead & Storage Tips

You can make these bars a day or two in advance—just keep them covered in the fridge. They’ll stay fresh for up to 4–5 days, and the flavour actually improves after a night in the fridge.

If you need to freeze them, do so before adding the icing sugar. Slice, wrap individually, and freeze for up to a month. Thaw in the fridge overnight.

FAQs About Rhubarb Custard Bars

Q: Can I use frozen rhubarb?

A: Yes—just thaw and drain it well so it doesn’t water down the custard.

Q: Can I double the recipe?

A: Absolutely! Use a 9x13 inch pan and adjust the baking time by an extra 5–10 minutes.

Q: Why did my custard split?

A: This is rare with this method, but overbaking can cause curdling. Keep an eye on that slight jiggle!

Q: Can I make this dairy-free?

A: Yes, though the texture will change. Use full-fat coconut milk in place of cream/milk and plant-based butter for the crust.

From My Kitchen to Yours

I always say rhubarb is one of those ingredients that deserves its moment in the spotlight. Every spring, when those ruby-red stalks show up at the market, I know it’s time to bring out this recipe. 

These custard bars are just the right mix of simple and show-stopping—whether you’re baking for guests or just because the sun came out.

Let me know if you bake them—I love seeing these bars on other people’s tables.

Happy baking!