Put the mushrooms into a bowl and pour over the boiling water.  Leave to soak for 20 minutes.

Heat the oil in a large pan, then add the onion and leek and cook over a medium heat for 10 minutes or until soft.

Strain the mushrooms, reserving the soaking liquid, and chop finely.  Add to the vegetables along with the pearl barley, then turn up the heat, season well and cook for 2 minutes, stirring frequently.

Add the lemon juice, white wine and rosemary sprig to the pan, season well, stir and allow to simmer for 5 minutes.  Now start to add the mushroom liquid about a ladleful at a time.  Turn the heat down but make sure the mixture is simmering gently at all times.  Keep stirring occasionally and adding mushroom liquid, so that the mixture does not stick to the pan.  If you run out of mushroom liquid, use boiling water.

When the barley is cooked but still has a chewy texture (about 20 minutes), add the sugar snaps, butter and half the Parmesan.  remove from the heat and allow to stand for 5 minutes, then season well and serve with the remaining Parmesan sprinkled over.