Pin It My neighbor showed up at my kitchen door one April morning with an armful of rhubarb stalks, their leaves still dewy and enormous. She said her garden had gone wild and would I please take some before it took over the fence. I had no plan, just a vague memory of my grandmother's crumble and a carton of milk in the fridge. What came out of the oven that afternoon was a happy accident: tangy fruit, silky custard, and that buttery crumble on top that nobody could stop picking at.
I brought a tray of these to a spring potluck once, still warm and barely set, because I ran out of time. People ate them with spoons straight from the pan, standing around the kitchen counter. Someone said it tasted like a British bakery in bar form. I've been making them every rhubarb season since, and now friends ask if it's time yet.
Ingredients
- Fresh rhubarb: Look for firm, bright stalks without too much browning, and always trim off the leaves since they're toxic.
- Granulated sugar for rhubarb: This tames the rhubarb's sharpness and helps it release its juices as it cooks down.
- Lemon juice: A little acid brightens the whole fruit layer and keeps the color vibrant.
- Cornstarch for rhubarb: This thickens the fruit mixture so it doesn't turn your bars soggy.
- All purpose flour: Forms the base and crumble, giving structure without being too heavy.
- Rolled oats: Adds texture and a rustic, homey chew to the crumble topping.
- Unsalted butter: Cold butter is key, it creates those lovely crumbly bits when you rub it in.
- Light brown sugar: Gives the crumble a deeper, almost caramel flavor compared to white sugar.
- Salt: Just a pinch balances all the sweetness and makes the butter taste richer.
- Whole milk: The custard needs the fat content to stay creamy and smooth.
- Egg yolks: These thicken the custard and give it that classic pale yellow color.
- Granulated sugar for custard: Sweetens the custard without overpowering the vanilla or fruit.
- Cornstarch for custard: Helps the custard set firm enough to slice cleanly once chilled.
- Vanilla extract: Stir it in at the end so the flavor stays bright and fragrant.
Instructions
- Prep your pan:
- Line your square pan with parchment, letting the edges hang over like little handles. This makes lifting the bars out later so much easier, trust me.
- Cook the rhubarb:
- Combine rhubarb, sugar, lemon juice, and cornstarch in a saucepan and cook over medium heat, stirring often, until it softens and thickens, about 8 to 10 minutes. Let it cool while you work on the base.
- Make the crumble mix:
- 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. It should clump when you squeeze it.
- Form the base:
- Press two thirds of the crumble mixture firmly into the bottom of your pan, packing it down with the back of a spoon. Save the rest for the top.
- Bake the base:
- Bake for 15 minutes at 180°C until lightly golden. It will firm up as it cools slightly.
- Prepare the custard:
- Heat the milk until steaming, then whisk egg yolks, sugar, and cornstarch in a bowl until smooth. Slowly pour in the hot milk while whisking, then return it all to the pan and cook, stirring constantly, until thick, about 2 to 3 minutes.
- Layer it up:
- Spread the cooled rhubarb over the baked base, then pour the custard over the fruit in an even layer. Sprinkle the reserved crumble on top.
- Bake until golden:
- Bake for 30 minutes, or until the crumble is golden and the custard is just set but still has a slight wobble. Let it cool completely in the pan.
- Chill and slice:
- Refrigerate for at least 2 hours before lifting out by the parchment and cutting into bars. Cold bars slice much cleaner.
Pin It One Sunday afternoon, I made these with my daughter, who was maybe six at the time. She was in charge of sprinkling the crumble on top, and she took it so seriously, tongue between her teeth, smoothing it out like frosting. When we cut into them the next day, she said they looked like a sunset. I think about that every time I see the pink rhubarb peeking through the custard.
Storing and Serving
These bars keep well in the fridge for up to three days, covered loosely with plastic wrap or in an airtight container. They actually taste better the next day once everything has settled and the flavors have mingled. Serve them cold, or let them come to room temperature for about 15 minutes if you prefer a softer custard. A dusting of powdered sugar or a small scoop of vanilla ice cream on the side turns them into a proper dessert.
Customizing the Flavor
If you want a bit more complexity, toss a handful of fresh raspberries in with the rhubarb before cooking. The raspberries break down and add a deeper berry note without making things too sweet. You can also swap the vanilla extract for almond extract in the custard, just use half the amount since almond is stronger. For a spiced version, add a pinch of ground ginger or cardamom to the crumble mixture.
Make Ahead and Freezing
You can bake these a day ahead and keep them chilled until you're ready to serve. They also freeze surprisingly well: wrap individual bars in parchment, then place them in a freezer bag for up to a month. Thaw them in the fridge overnight before serving.
- Freeze bars individually so you can grab just one or two at a time.
- Let them thaw slowly in the fridge to keep the custard smooth.
- Dust with powdered sugar right before serving for a fresh look.
Pin It These bars remind me that the best recipes often come from what's in season and what's handed to you unexpectedly. Keep them simple, let the rhubarb shine, and don't overthink it.
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 filling from becoming too watery. You may need to cook it slightly longer to achieve the proper thickness.
- → How do I know when the custard layer is properly set?
The custard should appear slightly jiggly in the center when you gently shake the pan, but not liquid. It will continue to set as it cools and chills in the refrigerator.
- → Can these bars be frozen for later?
Yes, these bars freeze well for up to 2 months. Wrap individual bars in plastic wrap, then place in an airtight container. Thaw overnight in the refrigerator 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 clean cuts much easier. Without chilling, the bars may be too soft and difficult to slice neatly.
- → Can I make these bars gluten-free?
Yes, substitute the all-purpose flour with a gluten-free baking blend and ensure your oats are certified gluten-free. The texture may be slightly different but still delicious.
- → What can I substitute for rhubarb if it's not in season?
Tart apples, plums, or a mix of berries work well as alternatives. Adjust the sugar according to the sweetness of your chosen fruit to maintain the balance of flavors.