Pin It My neighbor showed up one April morning with a bundle of rhubarb stalks from her garden, insisting I take them before they went to waste. I'd never baked with rhubarb before, but the idea of pairing its sharpness with something sweet and comforting felt right. After a bit of trial and error, these bars emerged: tangy fruit, silky custard, and a crumble that crackled under my fingernail. They disappeared within hours at a small gathering, and I've been making them every spring since.
I once brought a tray of these to a weekend book club, and someone asked if I'd trained in pastry. I laughed and admitted I'd burned the first batch because I forgot to set a timer. But that mistake taught me to watch the crumble closely in the final minutes: golden is perfect, but brown means you've gone too far. Now I pull them out right when the edges start to bubble and the top looks like toasted oats.
Ingredients
- Fresh rhubarb (400 g): Choose firm, bright stalks and trim away any leaves, which are toxic, then chop into small pieces so they cook down evenly and release their tart juice.
- Granulated sugar (75 g for rhubarb): This tames the rhubarb's sharp bite without making it overly sweet, and it helps draw out moisture as it cooks.
- Lemon juice (1 tbsp): A splash brightens the fruit layer and keeps the color vibrant instead of muddy.
- Cornstarch (1 tbsp for rhubarb, 2 tbsp for custard): This thickens both the fruit filling and the custard, preventing runny layers that would soak the crumble.
- All-purpose flour (250 g): Forms the base of the shortbread crumble, giving it structure and a tender, buttery bite.
- Rolled oats (100 g): Adds texture and a gentle chew to the crumble topping, making it more interesting than plain flour alone.
- Unsalted butter (150 g, cold and cubed): Cold butter is key, it creates those crumbly pockets that turn golden and crisp in the oven.
- Light brown sugar (100 g): Brings a hint of caramel sweetness to the crumble and helps it toast beautifully.
- Salt (1/2 tsp): Balances the sweetness and sharpens all the other flavors without being noticeable.
- Whole milk (300 ml): The foundation of the custard, providing richness and a creamy mouthfeel.
- Egg yolks (2 large): These thicken the custard and give it that classic silky texture and pale yellow color.
- Granulated sugar (60 g for custard): Sweetens the custard just enough to complement the tart rhubarb without overpowering it.
- Vanilla extract (1 tsp): A warm, fragrant note that ties the custard and crumble together and makes the whole kitchen smell amazing.
Instructions
- Prepare the pan and oven:
- Preheat your oven to 180°C (350°F) and line a 23cm square baking pan with parchment paper, leaving some overhang on the sides so you can lift the finished bars out easily. This step saves you from wrestling with a spatula later.
- Cook the rhubarb filling:
- In a saucepan, combine the chopped rhubarb, sugar, lemon juice, and cornstarch, then cook over medium heat, stirring often, until the rhubarb breaks down and the mixture thickens into a jammy consistency, about 8 to 10 minutes. Set it aside to cool while you work on the crumble.
- Make the crumble mixture:
- In a large bowl, mix the flour, oats, brown sugar, and salt, then rub in the cold cubed butter with your fingertips or a pastry cutter until the mixture looks like coarse breadcrumbs with some larger pea-sized pieces. Don't overwork it, you want those buttery pockets to stay distinct.
- Form the base:
- Press two-thirds of the crumble mixture firmly and evenly into the bottom of your prepared pan, packing it down with the back of a spoon or your palm. Reserve the remaining crumble in the bowl for the topping.
- Bake the base:
- Slide the pan into the oven and bake for 15 minutes, until the edges are lightly golden and the base feels firm to the touch. Remove it and let it cool slightly while you prepare the custard.
- Make the custard:
- Heat the milk in a saucepan until it steams but doesn't boil, then in a separate bowl, whisk the egg yolks, sugar, and cornstarch until smooth. Gradually pour the hot milk into the egg mixture, whisking constantly to avoid scrambling, then return everything to the pan and cook over medium heat, stirring continuously, until the custard thickens enough to coat the back of a spoon, about 2 to 3 minutes, then remove from heat and stir in the vanilla.
- Assemble the layers:
- Spread the cooled rhubarb filling evenly over the baked base, then pour the warm custard over the rhubarb, gently spreading it to cover. Sprinkle the reserved crumble mixture evenly over the top, letting it fall naturally for a rustic look.
- Bake until golden:
- Return the pan to the oven and bake for 30 minutes, or until the crumble is deeply golden and the custard is just set with a slight wobble in the center. The edges should look firm and lightly bubbling.
- Cool and chill:
- Let the bars cool completely in the pan at room temperature, then cover and chill in the refrigerator for at least 2 hours before lifting out by the parchment overhang and cutting into squares. This chilling step firms up the custard and makes clean slicing possible.
Pin It One Sunday afternoon, my sister and I sat on the back porch with these bars and cups of tea, watching her toddler chase a butterfly across the lawn. She said the custard reminded her of the school puddings we used to love, and the rhubarb tasted like summer at our grandmother's house. It's funny how a simple dessert can pull you back to moments you didn't realize you'd tucked away.
Choosing and Preparing Rhubarb
Look for stalks that are firm and brightly colored, either red or pink, and avoid any that feel limp or have brown spots. Trim off the leafy tops completely since they contain oxalic acid and aren't safe to eat, then wash the stalks and chop them into pieces about half an inch long. If your rhubarb is very thick, slice the stalks in half lengthwise before chopping so everything cooks at the same rate. I've learned that older, thicker stalks can be stringy, so peeling away the outer layer with a vegetable peeler helps create a smoother filling.
Getting the Custard Just Right
The custard should be thick enough to hold its shape when spread but still pourable, like a loose pudding. If it gets too thick, whisk in a splash of milk off the heat to loosen it before pouring. I once made the mistake of letting it boil, and it turned grainy and separated, so keep the heat at medium and stir constantly once the milk goes in. A silicone whisk works beautifully here because it scrapes the bottom of the pan and prevents sticking. If you do end up with a few lumps, strain the custard through a fine sieve before layering it over the rhubarb.
Serving and Storing
These bars are wonderful straight from the fridge, with the custard cool and firm, or you can let them sit at room temperature for ten minutes to soften the crumble slightly. A light dusting of powdered sugar makes them look elegant, and a scoop of vanilla ice cream turns them into a proper dessert. I've also served them with a dollop of whipped cream or a drizzle of honey, which plays nicely with the tartness of the rhubarb.
- Store the bars in an airtight container in the refrigerator for up to three days, layering parchment between them if you stack them.
- If you want to add raspberries, fold 50 to 75 grams into the cooked rhubarb for extra fruitiness and a deeper pink color.
- For a gluten-free version, swap the all-purpose flour for a gluten-free blend and use certified gluten-free oats.
Pin It These bars have become my go-to whenever rhubarb season arrives, and I love how they manage to taste both nostalgic and fresh at the same time. I hope they bring a little brightness to your kitchen, whether you're sharing them or sneaking one with your morning coffee.
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 bars 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. It will firm up further during chilling in the refrigerator.
- → Can I make these bars ahead of time?
Absolutely. These bars taste even better the next day after the flavors meld together. Store covered in the refrigerator for up to 3 days.
- → What can I substitute for rhubarb if it's not in season?
Try using tart apples, plums, or a mix of berries. Adjust sugar levels based on the sweetness of your chosen fruit.
- → Why do I need to chill the bars before cutting?
Chilling allows the custard to set completely and makes cutting clean, even bars much easier. The texture also improves with proper chilling.
- → Can I make the crumble mixture in advance?
Yes, prepare the crumble mixture and store it in the refrigerator for up to 2 days, or freeze for up to a month before using.