This is the ultimate soup-stew, an economical one-pot dish to be eaten with a spoon on a cold day in the Welsh uplands. Vary the vegetables as you please. The barley will need to be soaked overnight. If you forget, replace it with pasta, cooked beans or rice.
Gently sweat the leek, carrot and celery in half the olive oil in a roomy saucepan. Add the barley with its soaking water and 2litres water. Bring to the boil and skim off any grey foam that rises. Add the herbs and simmer for about 30 minutes, till the barley is soft.