Cabbage stuffed with mushrooms

Soak the pearl barley overnight. Soak the mushrooms in 1 cup cold water for several hours. Drain and slice the mushrooms retaining the mushroom liquid. Wash the barley thoroughly. Once drained boil it gently in a closed saucepan in the mushroom liquid until all the liquid has been absorbed. Soften the finely chopped onion and mushrooms in butter on a medium heat, season and add the pearl barley. Remove the outer cabbage leaves and stick a fork in the stalk. Put the cabbage head into salted boiling water and boil for a few minutes. Cut off a leaf and place it in iced water. Cut off another leaf and repeat the process until all the leaves have been cut. Remove the leaves from the water, dry them and trim the tough stems with a sharp knife. To make the rolls: lay 1tbsp of filling on a leaf and roll it up tucking in the sides. Fry the rolls in butter on a medium heat on both sides for 2-3 minutes. Steam for 15 minutes. Pour over some mustard oil and serve with sour cream.