Combine the cream and milk in a small saucepan and add 1 tsp of vanilla extract. Bring to the boil over a medium heat and then reserve to one side.
Meanwhile, whisk together the egg yolks with 60g of the caster sugar in a separate bowl until pale and thick. Gently bring the milk and cream back to the boil and then pour over the egg yolks and sugar whisking simultaneously.
Return the mixture to the saucepan and cook over a low heat, stirring continuously with a wooden spoon until it thickens and coats the back of the wooden spoon; usually 6-8 minutes. Remove from the heat and transfer to a clean bowl and allow to cool.
Meanwhile, place the rhubarb, remaining caster sugar, vanilla extract and water in a medium saucepan and bring to a simmer over a medium heat, stirring occasionally. Once at a simmer, lower the heat and cook for 10 minutes until the rhubarb is soft. Remove the rhubarb from the pan using a slotted spoon and transfer to a bowl.
Reduce the cooking liquor by half and then pour back over the rhubarb, mashing well until you have a purée. Strain through a sieve and collect in a bowl.
Once the custard mixture is cool, churn in an ice cream machine until it just starts to thicken. At this point pour in the rhubarb purée and churn for a further 10-15 minutes until soft and thickened. Serve two scoops in each serving glass.
*This pudding is very rich and indulgent, so it shouldn't be eaten too often. But it's perfect for those special occasions.