Save to Pinterest My neighbor used to drop off bundles of rhubarb every May, more than anyone could reasonably use. I started experimenting just to keep up, and these bars were born out of equal parts gratitude and desperation. The tang of rhubarb against sweet custard reminded me of the boiled sweets my grandmother kept in a glass jar. Now I make them every spring whether or not anyone leaves rhubarb on my doorstep.
I brought these to a garden party once, still cool from the fridge, and they disappeared before the tea was poured. Someone asked if I'd trained at a bakery. I laughed and said no, just a kitchen with too much rhubarb and a willingness to layer things hopefully.
Ingredients
- Fresh rhubarb (400 g, trimmed and chopped): Use the deep pink stalks if you can find them, they cook down into a jewel-toned layer that looks as good as it tastes.
- Granulated sugar (75 g for rhubarb, 60 g for custard): Balances the sharp bite of rhubarb without making it cloying, let the fruit speak for itself.
- Lemon juice (1 tbsp): Brightens the rhubarb and keeps the flavor lively, don't skip this even if it seems small.
- Cornstarch (1 tbsp for rhubarb, 2 tbsp for custard): Thickens both layers so they hold their shape when you slice, no runny middles here.
- All-purpose flour (250 g): Forms the tender base and crumbly topping, the foundation that holds everything together.
- Rolled oats (100 g): Adds texture and a rustic chew to the crumble, I like the way they toast golden on top.
- Unsalted butter (150 g, cold and cubed): Cold butter is key, it creates those flaky crumbs that melt into buttery pockets as they bake.
- Light brown sugar (100 g): Gives the crumble a hint of caramel warmth, white sugar works but this tastes deeper.
- Salt (1/2 tsp): A small pinch that makes every sweet note sing louder.
- Whole milk (300 ml): The base of a proper custard, full-fat is non-negotiable if you want it creamy.
- Large egg yolks (2): The richness and body of the custard come from here, save the whites for meringue another day.
- Vanilla extract (1 tsp): Pure vanilla is worth it, the warmth rounds out the custard and makes the whole kitchen smell like a hug.
Instructions
- Prepare your pan and preheat:
- Set your oven to 180°C (350°F) and line a 23cm square pan with parchment, letting the edges hang over like handles. This makes lifting the bars out later so much easier.
- Cook the rhubarb filling:
- Combine rhubarb, sugar, lemon juice, and cornstarch in a saucepan over medium heat, stirring often until the fruit breaks down and thickens into a glossy, jammy mixture, about 8 to 10 minutes. Let it cool while you work on the base.
- Make the crumble mixture:
- Mix flour, oats, brown sugar, and salt in a large bowl, then rub in the cold butter with your fingertips until it looks like damp sand with pea-sized bits. Keep some of the butter chunks visible, they make the crumble flakier.
- Form and bake the base:
- Press two-thirds of the crumble firmly into the bottom of your prepared pan, packing it down with the back of a measuring cup works well. Bake for 15 minutes until the edges just start to turn golden.
- Prepare the custard:
- Heat the milk in a saucepan until it steams, 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 thickened like pudding, about 2 to 3 minutes. Stir in vanilla off the heat.
- Layer and top:
- Spread the cooled rhubarb evenly over the baked base, then gently pour the custard over the fruit. Sprinkle the reserved crumble over the top in an even layer.
- Bake until golden:
- Return the pan to the oven and bake for 30 minutes, until the crumble is deeply golden and the custard is just set with a slight wobble in the center. Let it cool completely in the pan, then chill for at least 2 hours before slicing.
Save to Pinterest 
Save to Pinterest The first time I served these at a family gathering, my aunt leaned over and whispered that they tasted like the rhubarb and custard sweets she used to buy as a girl. That felt like the best compliment I've ever received in a kitchen.
Storing and Serving
These bars keep beautifully in the fridge for up to three days, covered loosely with foil or in an airtight container. I like them cold, straight from the fridge, when the custard is firm and the crumble has softened just slightly. They're lovely with a pot of tea or packed into a lunchbox for a midday surprise.
Variations and Tweaks
If you want a bit more fruit complexity, toss a handful of raspberries in with the rhubarb while it cooks. The berries break down and add a deeper pink color and a hint of sweetness. You can also swap the vanilla extract for almond extract in the custard if you like that marzipan-like warmth.
Finishing Touches
A light dusting of powdered sugar over the top makes them look bakery-ready, or serve them with a small scoop of vanilla ice cream for contrast. I've also drizzled them with a little honey when I'm feeling fancy.
- Use a sharp knife wiped clean between cuts for neat, professional-looking bars.
- Let the bars sit at room temperature for 10 minutes before serving if you want the flavors to open up.
- If you're making these ahead, they actually taste better the next day once everything has settled together.
Save to Pinterest 
Save to Pinterest These bars have a way of making springtime feel special, even on ordinary afternoons. I hope they bring a little brightness to your table too.
Recipe Questions & Answers
- → Can I use frozen rhubarb instead of fresh?
Yes, frozen rhubarb works well. Thaw and drain excess liquid before cooking to prevent the filling from becoming too watery. You may need to cook it slightly longer to achieve the right consistency.
- → How do I know when the custard layer is properly set?
The custard should have a slight wobble in the center when you gently shake the pan. It will continue to set as it cools. Overbaking can cause the custard to curdle or become grainy.
- → Can these bars be frozen for later?
Yes, these bars freeze well for up to 2 months. Wrap individual bars tightly in plastic wrap and store in an airtight container. Thaw in the refrigerator overnight before serving.
- → What can I substitute for rhubarb if it's out of season?
Try tart fruits like cranberries, sour cherries, or a mix of raspberries and blackberries. Adjust sugar to taste depending on the sweetness of your chosen fruit.
- → Why is chilling important before cutting?
Chilling allows the custard to firm up completely, making it much easier to cut clean, neat bars. Cutting while warm will result in messy, uneven pieces with filling that runs.
- → Can I make the components ahead of time?
Absolutely. You can prepare the rhubarb filling and custard up to a day in advance and store them separately in the refrigerator. Assemble and bake when ready to serve.