Wash and trim the rhubarb, then cut into 2.5cm (1in) pieces. Put in a heavy-bottomed pan with the sugar and grated ginger.
In a jug, mix the cordial with 750ml (1¼ pints) of water. Add 50ml of this mixture to the rhubarb, then stew over a medium heat with a lid on for 5-8mins.
When the rhubarb is cooked add the rest of the cordial and bring it to the boil.
Put the gelatine leaves into a bowl of cold water for 4mins to soften.
Take the rhubarb mixture off the heat. Remove the gelatine from the water, squeeze out any excess liquid, and add the gelatine to the mixture. Stir thoroughly for 1min until the gelatine has melted.
Cool, then ladle into four glasses. Put into the fridge to set for 4-6 hours, then serve.
See more Dessert recipes