Roughly clean, and top and tail the beetroot (cut the roots and stalk from the beetroot).
Place in a large pot and boil until the skin comes away. To test this use a pair of tongs to remove the veggie from the pot and press down with your thumb and move in a downward motion. The skin will just come away.
Carefully drain the boiling water and run until cold water. Remove all the beetroot skins. This process does stain your hands so you could wear gloves.
Use a food processor or a grater to grate the beetroot and onions, and place in to a large pot or jam pan.
Add the sugar, cardamom, pepper, salt and vinegar and simmer for 20 minutes.
Make a slurry of cornflour and vinegar (an additional 2 Tbsp of vinegar) and add to the relish. Simmer for an additional 5 minutes until the mixture thickens.
Steralise your jars and add the hot mixture in to the hot jars. Place on the lids (or cellophane covers) and allow to cool.