Rhubarb and Custard Crumble Bars (Printable Version)

Tangy rhubarb and vanilla custard layered beneath golden buttery crumble. A delightful British springtime treat.

# What You'll Need:

→ Rhubarb Layer

01 - 14 oz fresh rhubarb, trimmed and chopped
02 - 5.3 oz granulated sugar
03 - 1 tablespoon fresh lemon juice
04 - 1 tablespoon cornstarch

→ Shortbread Base and Crumble

05 - 8.8 oz all-purpose flour
06 - 3.5 oz rolled oats
07 - 5.3 oz unsalted butter, cold and cubed
08 - 3.5 oz light brown sugar
09 - 1/2 teaspoon salt

→ Custard Layer

10 - 10.1 fl oz whole milk
11 - 2 large egg yolks
12 - 2.1 oz granulated sugar
13 - 2 tablespoons cornstarch
14 - 1 teaspoon vanilla extract

# How to Make It:

01 - Preheat oven to 350°F. Line a 9-inch square baking pan with parchment paper, leaving overhang for easy removal.
02 - In a saucepan, combine rhubarb, sugar, lemon juice, and cornstarch. Cook over medium heat, stirring frequently, until rhubarb softens and mixture thickens, approximately 8 to 10 minutes. Set aside to cool.
03 - In a large bowl, mix flour, oats, brown sugar, and salt. Rub in cold butter with your fingers or pastry cutter until mixture resembles coarse breadcrumbs.
04 - Press two-thirds of crumble mixture firmly into prepared pan to form even base. Reserve remaining crumble for topping.
05 - Bake base for 15 minutes until lightly golden. Remove from oven and allow to cool slightly.
06 - Heat milk in saucepan until steaming but not boiling. In a bowl, whisk egg yolks, sugar, and cornstarch until smooth. Gradually pour hot milk into egg mixture, whisking constantly. Return to saucepan and cook over medium heat, stirring, until thickened, approximately 2 to 3 minutes. Remove from heat and stir in vanilla extract.
07 - Spread cooked rhubarb evenly over baked base. Pour custard layer over rhubarb.
08 - Sprinkle reserved crumble mixture evenly over custard layer.
09 - Bake for 30 minutes, or until crumble is golden and custard is just set.
10 - Cool completely in pan, then refrigerate for at least 2 hours before lifting out and cutting into bars.

# Expert Tips:

01 -
  • It balances tart rhubarb with silky vanilla custard in a way that feels both comforting and bright.
  • The buttery oat crumble on top adds crunch without being too sweet or heavy.
  • These bars slice cleanly once chilled, making them perfect for sharing or packing up for picnics.
  • You can prep the layers ahead and assemble them when you have time to bake.
02 -
  • Don't skip chilling the bars, they're nearly impossible to cut neatly when warm and the custard needs time to fully set.
  • If your rhubarb is especially tart, taste the cooked mixture and add a bit more sugar before layering it in.
  • Cold butter is essential for a crumbly topping, if it's too soft, the mixture will clump instead of scatter.
  • Whisk the custard constantly while it cooks or it can seize up and turn lumpy in seconds.
03 -
  • Line your pan with enough parchment overhang so you can lift the whole slab out easily, it makes cutting clean bars so much simpler.
  • Let the custard cool for a minute or two before pouring it over the rhubarb, or it can disturb the fruit layer and make things messy.
  • If the top crumble starts browning too fast, tent the pan loosely with foil for the last 10 minutes of baking.
  • Use a sharp knife dipped in hot water and wiped dry between cuts for the neatest slices.
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