Rhubarb and custard choux buns

For the jam, add the rhubarb, lemon juice and sugar to a large saucepan and stir to combine. Split open the vanilla pod lengthways and scrape out the seeds. Add both the seeds and the pod itself to the saucepan and stir to combine

Place over a high heat and cook, stirring frequently, until the jam reaches 104°C. Leave to cool, then transfer to a piping bag and store in the fridge until needed

Next, make the crème diplomat. Add the milk and vanilla to a pan and gently warm (do not allow to boil). In a separate bowl, beat the sugar, cornflour and egg yolks together until smooth

When the milk is steaming hot, gradually pour it into the egg mixture, whisking constantly. Once it’s all combined, pour the mixture back into the saucepan and gently cook, whisking constantly, for 1-2 minutes until thickened. Remove from the heat, beat in the butter, then immediately cover with cling film, ensuring it’s touching the surface of the custard (otherwise a skin will form). Once cool, transfer to the fridge to chill

To make the craquelin, put the flour, sugar and a large pinch of fine sea salt in a bowl and mix to combine. Add the butter and rub together until a crumbly dough is formed. Gently press together to form a uniform dough with no lumps of butter. Place the dough between 2 sheets of baking paper and roll out to a thickness of 2mm. Freeze until needed

Preheat the oven to 190ºC and line a large baking tray with baking paper

To make the choux, place the water and milk into a saucepan and mix in the salt, sugar and butter. Place over a low-medium heat and cook until the butter has melted. Turn up the heat and bring the liquid to a rolling boil

Remove the pan from the heat and pour in the flour in one go, mixing immediately to form a soft dough. Place the pan back on the heat and cook for 1-2 minutes more until the dough leaves a fine film on the base of the pan

Scrape the dough into a bowl and beat for a few minutes to allow it to cool slightly, then beat in the eggs, a little at a time, waiting for them to incorporate into the dough before adding more (it may look split at first, but keep beating and the eggs will combine properly)

Scrape the choux dough into a piping bag fitted with a small round piping tip, no more than 1cm wide. Pipe rounds, about 4–5 cm in diameter onto the lined tray, leaving plenty of space for the choux to expand

Remove the craquelin from the freezer and peel back the top layer of paper. Use a round cookie cutter, the same size as your rounds of choux, to cut out discs of the craquelin. Place a disc on top of each mound of choux

Bake the choux buns for 30 minutes until golden. Turn off the oven and open the oven door briefly to release any steam. Close the door and allow the buns to cool slowly, in the still-warm oven, for 20–30 minutes

Remove the pastry cream from the refrigerator and beat until smooth. Pour the cream into a large bowl and whisk by hand or with an electric mixer until it holds soft peaks. Fold the cream into the pastry cream. Scrape into a piping bag fitted with a star shaped piping tip

Use a small serrated knife to slice a hole in the base of each bun. Fill each bun with the cream, then add some of the rhubarb jam. Finish by piping a little of the creme diplomat and jam on top of each bun