Wash and trim the rhubarb and chop into 2 inch pieces.
In a small saucepan, combine the rhubarb, sugar and water. Bring to a boil and stir to make sure the sugar has all dissolved. Reduce the heat and simmer until the rhubarb is tender.
In a small bowl combine the gelatine powder with the 2 tbsp of cold water. Allow to sit for a minute for the gelatine to absorb the water then microwave for 10 seconds so it is fully dissolved.
Pour the gelatine mixture into the rhubarb and stir to combine fully then set aside to cool to room temperature.
Add the bottle of ginger beer to the mixture, stir and divide into serving glasses. Refrigerate until set.
Serve with whipped cream and a sprinkle of chopped crystalized ginger.