Rhubarb and custard crumble tart

Method

1. For the pastry, put the flour in a blender with the custard powder and a good pinch of salt. Whizz briefly, then add the butter. Pulse until the mix resembles fine breadcrumbs. Transfer to a big bowl and stir in the sugar. Add the egg yolks and 3-4 tbsp ice-cold water. Quickly mix together, then shape into a flat disc, wrap in cling film and chill for 30 minutes.
2. Preheat the oven to 200°C/fan180°C/ gas 6 and pop a baking sheet inside to heat up. For the crumble, put the flour and a pinch of salt in a bowl, add the butter and rub together with your fingers until the mix resembles coarse breadcrumbs. Stir in the sugar, then scatter over a shallow baking tray. Set aside.
3. Roll out the pastry on a floured work surface and use to line a 21cm, loose-bottomed, fluted tart tin that’s 3.5cm deep. Trim any excess pastry and prick the base all over with a fork. Line with baking paper and fill with baking beans or rice. Bake for 10 minutes on the hot baking sheet. Remove the paper and beans/rice, and bake for 5 minutes more until the pastry is crisp. Remove from the oven and set aside. Leave the oven on.
4. Make the custard filling. Mix the eggs and egg yolks, 60g of the caster sugar, orange zest and cornflour together in a bowl. Put the cream, 1 split vanilla pod and seeds in a pan over a medium heat and bring almost to the boil. Slowly strain the hot cream over the egg mixture, stirring. Pour back into the cleaned pan and return to the hob. Heat gently, stirring, until the custard is thick enough to coat the back of a spoon. Pour into a jug, then cover the surface with cling film to stop a skin forming. Cool and chill.
5. Place the rhubarb in a bowl, stir in the remaining 75g caster sugar and the seeds from the remaining vanilla pod, scatter over a shallow baking tray, dot with butter, drizzle with 1 tbsp water and add the vanilla pod. Roast for 15 minutes. Put a colander over a bowl, then pour the rhubarb into the colander, discarding the vanilla pod. Reserve the juices and allow the rhubarb to cool a little.
6. Pour the custard into the pastry case, then top with the rhubarb, poking it under the custard a little. Bake on the baking sheet for 12-15 minutes until the custard is just set. Put the crumble topping in the oven at the same time, shaking its tray occasionally, cooking for the same amount of time until crunchy and golden. Remove both from the oven. Carefully remove the tart from the tin. Scatter with the crumble and some of the reserved rhubarb juice. Serve warm or at room temperature.