Heat the oil in a saucepan and add the celery, leeks and carrot. Cook over a medium heat for 5 minutes.
Stir in the pearl barley, stock and mustard, season to taste and simmer for 20–25 minutes. Add the mangetout, if liked, and simmer for 5 minutes.
Ladle into warmed soup bowls and serve piping hot.
Notes / Tips / Wine Advice:
For winter vegetable broth, make up the soup as above using just 1 chopped leek and adding 125 g (4 oz) finely diced swede. Simmer for 20 minutes then add 125 g (4 oz) finely shredded green cabbage instead of the mangetout. Simmer for 10 minutes then ladle into bowls and top with diced crispy grilled bacon.