Wash and cut rhubarb stalks in 2" sections, put them in the bowl of a food processor and process until then turn into a pulp. Push it through a fine sieve with a spoon to extract all the juice, then discard the pulp. You should get about 300 ml/ 1 ¼ cup of rhubarb juice.
In a food processor or blender mix eggs, sugar and cornflour/corn starch until you have a homogenous mixture with no lumps remaining. Alternatively you can do this step by hand using a bowl and a whisk.
In a saucepan combine 1 cup of rhubarb juice, egg, sugar and corn starch mixture and cubed butter, set the pan over low heat and star cooking it while stirring with a whisk the entire time until butter melts and the curd thickens. Do not turn the heat up to speed up the process or the eggs will turn into scrambled eggs and the curd go lumpy!
Take off the heat when the curd is the consistency of thick sour cream. You may push it through a fine sieve again to ensure there are no lumps and the curd is silky smooth. Add the remaining rhubarb juice to increase the tart flavour of the rhubarb and a drop of pink food colouring if desired as the curd loses its colour when cooks!
Chill in the fridge for at least 3 hours or overnight. The rhubarb curd will thicken when chilled.
Notes
This recipe makes approximately 600 ml/ 2.5 cups of rhubarb curd.