Rhubarb and custard tart

Name: Rhubarb and custard tart
Ingredients: 250g/9oz plain flour, plus extra for rolling; 150g/5½oz cold butter, cut into cubes; 1 medium free-range egg, beaten with 1 tbsp cold water; 3 medium free-range eggs; 2 medium free-range egg yolks; 100g/3½oz caster sugar; 300ml/10fl oz whole milk; 300ml/10fl oz double cream, plus extra to pour; 1 vanilla pod, split lengthways and seeds scraped out; 65g/2¼oz caster sugar, plus extra to taste; 400-500g/14oz-17oz rhubarb (preferably forced rhubarb), trimmed