Save to Pinterest My neighbor handed me an armful of rhubarb stalks over the fence one Saturday morning, more than I knew what to do with. I'd been craving something layered and comforting, something that reminded me of the custard tarts my gran used to make but easier to share. These bars came together that afternoon, filling the kitchen with the smell of buttery oats and tart fruit bubbling away. The custard settled into the rhubarb like they'd been waiting to meet, and the crumble on top turned the exact shade of golden I'd hoped for. I brought a plate to my neighbor the next day, and she asked for the recipe before I even made it to her porch.
I made these for a spring potluck once, and they disappeared faster than anything else on the table. Someone asked if I'd bought them from a bakery, which made me laugh because I'd been worried the custard looked a little wobbly when I set the pan down. A friend told me later she'd never liked rhubarb until that day, and now she grows it in her own garden. It's funny how a simple dessert can change someone's mind about an ingredient they'd written off years ago. I still think about that conversation every time I trim fresh rhubarb stalks.
Ingredients
- Fresh rhubarb: The star of the show, bringing that sharp, fruity tang that softens beautifully when cooked with sugar and lemon.
- Granulated sugar (for rhubarb): Just enough to tame the tartness without turning it into jam.
- Lemon juice: Brightens the rhubarb and keeps the flavor lively, not flat.
- Cornstarch (for rhubarb): Thickens the fruit so it doesn't make the base soggy.
- All-purpose flour: The backbone of both the base and the crumble, giving structure without heaviness.
- Rolled oats: Add texture and a slight chew that makes the crumble feel homemade and hearty.
- Unsalted butter: Cold and cubed is key so it creates those flaky, crumbly bits when rubbed into the dry ingredients.
- Light brown sugar: Adds a gentle molasses note that complements the oats and butter.
- Salt: Balances the sweetness and makes every other flavor come forward.
- Whole milk: Creates a rich, smooth custard that doesn't taste thin or watery.
- Egg yolks: Give the custard its silky texture and pale yellow color.
- Granulated sugar (for custard): Sweetens gently without overpowering the vanilla.
- Cornstarch (for custard): Thickens the custard quickly and evenly, no lumps if you whisk well.
- Vanilla extract: The quiet warmth that ties the custard and fruit together.
Instructions
- Prep your pan:
- Preheat your oven to 180°C and line a 23cm square pan with parchment, leaving enough overhang to lift the bars out later. This one step will save you so much frustration when it's time to slice.
- Cook the rhubarb:
- Combine the chopped rhubarb, sugar, lemon juice, and cornstarch in a saucepan over medium heat, stirring often until the fruit softens and the mixture thickens, about 8 to 10 minutes. Let it cool while you work on the base so it doesn't melt the custard later.
- Make the crumble mix:
- Mix flour, oats, brown sugar, and salt in a large bowl, then rub in the cold butter with your fingertips or a pastry cutter until it looks like coarse sand with some pea-sized bits. The colder the butter, the better the texture.
- Form the base:
- Press two-thirds of the crumble firmly into the bottom of your lined pan, making it as even as you can. Save the rest for the topping.
- Bake the base:
- Pop the base in the oven for 15 minutes until it's lightly golden and smells buttery. Let it cool slightly before layering.
- Prepare the custard:
- Heat the milk in a saucepan until steaming, then whisk egg yolks, sugar, and cornstarch in a bowl until smooth. Slowly pour the hot milk into the yolk mixture while whisking constantly, then return everything to the pan and cook over medium heat, stirring, until thick, about 2 to 3 minutes. Stir in vanilla off the heat.
- Layer it up:
- Spread the cooled rhubarb evenly over the baked base, then pour the warm custard over the fruit. Work gently so the layers stay distinct.
- Top with crumble:
- Sprinkle the reserved crumble mixture evenly over the custard layer. Don't press it down, just let it sit loose and craggy.
- Bake again:
- Return the pan to the oven and bake for 30 minutes, until the crumble is golden and the custard just barely jiggles in the center. It will set more as it cools.
- Chill and slice:
- Let the bars cool completely in the pan, then chill for at least 2 hours before lifting out by the parchment and cutting into squares. Cold bars slice cleanest.
Save to Pinterest I served these at a tea party my mum hosted for her book club, and one of the women said they reminded her of childhood summers in Yorkshire. She hadn't tasted rhubarb and custard together in decades, and I watched her close her eyes after the first bite. Food has this quiet way of carrying people back to moments they thought they'd forgotten. That afternoon, I realized these bars weren't just dessert, they were a little edible time machine.
Storing and Serving
These bars keep beautifully in the fridge for up to three days, covered loosely with foil or in an airtight container. The custard stays creamy and the crumble softens just enough to blend with the layers without losing its texture entirely. I like them cold straight from the fridge, but some people prefer them at room temperature for about 15 minutes so the flavors open up. A light dusting of powdered sugar or a small scoop of vanilla ice cream turns them into something a bit more special for guests.
Variations to Try
If you want a sharper, fruitier edge, toss a handful of fresh raspberries in with the rhubarb before cooking. Strawberries work too, though they're sweeter and less tangy. I once stirred a pinch of ground ginger into the crumble mixture, and it added a subtle warmth that paired beautifully with the custard. You could also swap half the oats for chopped almonds if you want a nuttier crunch. Just remember that any changes to the fruit layer might affect how much liquid cooks off, so keep an eye on the thickness.
What to Watch For
The custard can curdle if you add the hot milk too quickly or cook it over heat that's too high, so whisk steadily and keep the temperature medium. If your rhubarb is very thick-stalked, chop it a bit smaller so it cooks evenly and doesn't leave crunchy bits. The crumble topping should look dry and crumbly, not wet or doughy, before it goes in the oven.
- Let the rhubarb cool completely before layering, or it will thin out the custard.
- Press the base firmly so it doesn't crumble apart when you slice the bars.
- Use fresh rhubarb if possible, frozen can release too much water and make the layers soggy.
Save to Pinterest These bars have become my go-to when I want to impress without spending all day in the kitchen. They look elegant, taste bright and comforting, and somehow manage to feel both nostalgic and new at the same time.
Recipe FAQs
- → Can I use frozen rhubarb instead of fresh?
Yes, frozen rhubarb works well. Thaw and drain excess liquid before cooking to prevent the mixture from becoming too watery.
- → How do I know when the custard layer is properly set?
The custard should be just set with a slight wobble in the center when gently shaken. It will firm up further during chilling.
- → Can these bars be frozen for later?
Yes, wrap individual bars tightly in plastic wrap and freeze for up to 2 months. Thaw in the refrigerator overnight before serving.
- → Why do I need to chill the bars before cutting?
Chilling allows the custard to fully set and the layers to firm up, making it much easier to cut clean, neat squares without the filling oozing out.
- → Can I substitute the rhubarb with other fruit?
Absolutely. Strawberries, raspberries, or mixed berries work beautifully. Adjust sugar based on the sweetness of your chosen fruit.
- → What's the best way to store leftover bars?
Store in an airtight container in the refrigerator for up to 3 days. The crumble topping may soften slightly but remains delicious.