Wash the rhubarb, trim and cut into short lengths of about 2cm (1in) long.
Place rhubarb, sugar, elderflower cordial into a preserving pan or very large saucepan and stir together to mix. Leave to stand for an hour or so.
When you are ready to make the jam, put a couple of saucers in the freezer for testing the set and sterilise 3 large jars.
Place the pan over a very low heat and heat gently until the juices begin to run and the sugar has dissolved, stirring constantly. Try not to splash up the side of the pan too much during this stage.
Once the sugar has completely dissolved (you will not hear and gritty scraping noise as you stir) turn up the heat and bring to a rolling boil. Once it has reached a good rolling boil, set the timer and boil for 8 minutes.
Take the pan off the heat and test for set by placing a few drops of jam onto one of the chilled saucers and chilling for a minute or two. If the setting point has still not been reached, boil for another 2 minutes and test again. Repeat if necessary until you have a set.
Pour into the sterilised hot jars and seal immediately. Label and store in a cool place until required
Notes For more details on sterilising jars and testing for set read my How tohere. Once open store the jam in the refrigerator for up to 3 months.Nutrition information is approximate and is meant as a guideline only.