Heat the vegetable oil in a large saucepan over a medium heat. Add the two finely chopped carrots, the onion and celery and cook for five minutes, or until soft. Add the flat ribs and 3 litres/5¼ pints of boiling water to the pan.
Bring back to the boil and add the pearl barley, split peas and bay leaves. Place a lid on the saucepan and reduce the heat. Simmer with the lid on for 1½ hours.
Taste and add a good pinch of salt and pepper, to taste. Add the lentils and cook for a further 20 minutes, making sure to replace the lid.
After 20 minutes, add the leeks, the reserved diced carrot, the turnip and the potatoes and cook for a further 20 minutes, or until tender.
Adjust the seasoning by adding salt and pepper if required.
Remove the flat ribs from the pan and set aside on a warm plate.
Ladle the broth into serving bowls and carve a piece of flat rib from the bone and place on top of the broth.