Start with the pastry. Rub the cold butter into the flour, sugar and salt until you have a rough breadcrumb texture. Add the egg yolk and enough cold water to bring it together into a dough. Flatten into a disc, wrap and chill for about 30 minutes.

While that rests, toss the rhubarb with the sugar, blood orange juice and zest and leave it to sit so it becomes glossy and lightly syrupy.

For the custard, warm the milk in a saucepan until just steaming. In a bowl whisk the egg yolks, sugar and cornflour together until smooth and pale, then slowly pour in the hot milk while whisking. Tip everything back into the pan and cook gently, stirring constantly, until very thick. Stir in the vanilla and butter and leave it to cool , it should be thick enough to hold its shape.

Heat the oven to 190°C / 170°C fan. Roll the pastry into a rough 30cm circle on baking paper and spread the custard in the centre, leaving a border of a few centimetres. Pile the rhubarb on top, leaving behind any excess juices in the bowl, then fold the pastry edges over the filling. Brush the pastry with beaten egg and scatter generously with demerara sugar. Drizzle the golden syrup or honey over the rhubarb.

Bake for 40–45 minutes until the pastry is deeply golden and the rhubarb soft and jammy. Leave it to sit for about 10 minutes before slicing so the custard settles slightly.