Equipment
Ingredients
Shortbread Base
- 160 g plain flour
- 50 g caster sugar
- 115 g unsalted butter, cold and cubed
- 2 g salt
Rhubarb Filling
- 400 g fresh rhubarb, trimmed and cut into 2cm pieces
- 80 g caster sugar
- 15 g cornflour
- 5 ml vanilla extract
Vanilla Custard
- 250 ml whole milk
- 100 ml double cream
- 4 egg yolks
- 60 g caster sugar
- 20 g cornflour
- 5 ml vanilla bean paste
Oat Crumble Topping
- 100 g rolled oats
- 75 g plain flour
- 75 g demerara sugar
- 80 g unsalted butter, cold and cubed
- 2 g ground cinnamon
- 1 g salt
Nutrition (per serving)
Method
Preheat your oven to 180°C/350°F. Line a 20x20cm square baking pan with parchment paper, leaving an overhang on the sides for easy removal later.
In a mixing bowl, combine the flour, sugar, salt, and cold cubed butter for the shortbread base. Rub the mixture together with your fingertips until it resembles coarse breadcrumbs, then squeeze lightly to bring it together into a crumbly dough.
Press the shortbread dough firmly and evenly into the base of the prepared baking pan. Bake for 15 minutes until lightly golden, then remove from the oven and set aside. Keep the oven turned on.
While the base bakes, prepare the filling. Toss the chopped rhubarb in a bowl with the caster sugar, cornflour, and vanilla extract until every piece is well coated.
For the custard, gently heat the milk and double cream in a saucepan over medium heat until it just begins to steam. Do not let it boil.
In a separate heatproof bowl, whisk the egg yolks, caster sugar, and cornflour until pale and smooth. Slowly pour the hot milk mixture into the eggs in a thin stream, whisking constantly to temper the eggs.
Pour the tempered egg mixture back into the saucepan. Cook over medium-low heat, whisking constantly, until the custard thickens significantly. Remove from heat and whisk in the vanilla bean paste.
To make the crumble topping, mix the rolled oats, plain flour, demerara sugar, cinnamon, and salt in a bowl. Rub in the cold cubed butter until the mixture clumps together in rustic, varied sizes.
Arrange the prepared rhubarb evenly over the baked shortbread base. Pour the warm thick custard directly over the rhubarb, spreading it into an even layer. Finally, scatter the oat crumble generously over the top.
Bake in the 180°C/350°F oven for 35 to 40 minutes, until the topping is deeply golden and the rhubarb juices are bubbling around the edges.
Allow the crumble to cool completely in the pan for at least 1 hour. This resting period allows the custard to set so it can be neatly sliced.
Chef's Notes
- Blind baking the shortbread base is essential to prevent a soggy bottom when the wet rhubarb and custard are added.
- For the cleanest slices, wait until the dessert is completely cold before cutting. If you prefer a warm, messy, pudding-style dessert, serve it 20 minutes out of the oven.
- Do not skip the cornflour in the rhubarb filling. Rhubarb releases a tremendous amount of liquid as it cooks, and the starch is necessary to create a jam-like consistency rather than a soup.
- Leaving the crumble topping in slightly larger, rustic clumps yields a much better crunch than breaking it down into a fine powder.
Storage
Refrigerator: 4 days — Keep in an airtight container to prevent the crumble topping from absorbing moisture.
Freezer: 1 month — Wrap tightly. Texture of the custard may change slightly upon thawing.
Reheating: Reheat portions in a 150C oven for 10-15 minutes to crisp the topping.
