Rhubarb and custard slice

Heat the oven to 180C/fan 160C/gas 4. Chop the rhubarb into chunks, then cut them lengthways along the grain, to get thin cross-sections. Spread evenly over a baking sheet covered in baking paper or a silicone mat. Sprinkle over 1 tbsp sugar. Cook for 20 minutes until the rhubarb looks dry, but soft. Tip into a small blender with another 1 tbsp sugar, or more if the rhubarb is tart. Blend to a purée, then cool.

Turn the oven up to 200C/fan 180C/gas 6.
Roll out the pastry on a sheet of baking paper to a 30x35cm rectangle. Dust with 2 tbsp icing sugar and lay over a second sheet of baking paper. Lift onto a baking sheet and sit another flat baking sheet on top. Weigh down with an ovenproof dish filled with baking beans, or something similarly heavy and ovenproof.

Bake for 30 minutes, or until the pastry is golden and crisp. Remove the weight, the top baking sheet and layer of baking paper. Leave to cool.

Scrape the vanilla seeds from the pod, add to the milk and bring to a gentle simmer. Whisk the egg yolks and sugar until fluffy, then whisk in the flours until smooth. Slowly pour the hot milk over the egg and sugar mix, continually whisking. Pour into a pan, and cook on a low heat, whisking until it thickens, and looks like a very thick custard. The custard needs to be thick enough to hold in the puff pastry, so cook on a very low heat for around 10 minutes, until when the whisk is removed from the custard, the ribbon it leaves stays on the surface and doesn’t disappear. Push through a sieve into a clean bowl. Cover with clingfilm, touching the surface of the custard (to prevent a skin forming). Cool completely, then chill until needed.

Whip the double cream until it holds peaks, reserve half, and fold the rhubarb purée gently through the remainder. You want it to be streaked with the pink. Spoon into a large piping bag with a 1cm plain nozzle and chill. Fold the remaining cream into the cooled custard gently, so it holds peaks, and put into another piping bag with a similar nozzle, chill.

When the pastry is cool, use a sharp knife and ruler to cut the pastry into twelve 8cmx5cm pieces. Pipe alternate blobs of the rhubarb cream over 6 of the pastry rectangles, and pipe blobs of custard in between. Gently sandwich on the remaining 6 puff pastry tops and chill until you’re ready to serve (they will keep for a few hours, any longer and the puff pastry will go soggy), sprinkle generously with a dusting of icing sugar to serve.