Wash and trim the rhubarb, then chop into 2-3cm pieces.
Place the rhubarb in a saucepan with the 200g caster sugar and the seeds from the vanilla pod (scrape out the seeds and add them to the rhubarb, then add the pod itself).
Cook over a medium heat for about 10-15 minutes, stirring occasionally, until the rhubarb has softened and released its juices.
Remove the vanilla pod and set the rhubarb aside to cool.
Whisk the egg yolks and 50g caster sugar together in a bowl until pale and creamy.
Heat the milk and double cream in a saucepan until just simmering.
Gradually pour the hot milk and cream mixture onto the egg yolk mixture, whisking constantly.
Pour the custard mixture back into the saucepan and cook over a low heat, stirring constantly with a wooden spoon, until the custard thickens enough to coat the back of the spoon.
Do not let the custard boil, or it will curdle.
Pour the custard into a clean bowl, cover with cling film (pressing it directly onto the surface of the custard to prevent a skin from forming), and chill in the refrigerator.
To serve, spoon the cooled rhubarb into serving bowls and top with the chilled custard.
