Photograph: Jonathan Buckley
Put the rhubarb in a large pan and add 1.5 litres of cold water (you don't want to cover it completely as this dilutes the flavour). Using a potato peeler, take 4 strips of orange skin from each orange; add this to the pan with the juice from both oranges and the star anise.
Bring the rhubarb to the boil, then turn down the heat and simmer gently until soft (it may look like mush at this stage). Take off the heat and allow to cool for an hour.
Pour the rhubarb and juice into a large jelly bag hanging over a large bowl (or through a sieve lined with a double layer of gauze or muslin) and allow the juice to drip through overnight.
Pour the strained juice into a pan and, on a low heat, add the sugar. Stir until dissolved.
You can add 2 teaspoons of citric acid at this stage if you want to store this for several months – this is not necessary if the cordial is going to be used straight away. The citric acid does give the cordial a good tart kick, or you can add the juice of 3 lemons for a sharper flavour.
Allow the cordial to cool. Pour into sterilised bottles and store in the fridge. Dilute to taste.
Recipe from Perch Hill