Place the barley in a saucepan and cover with water. Add salt, pepper and bay leaf, bring to a boil, reduce heat and simmer 30 minutes or until tender. Remove bay leaf.
Core the cabbage and simmer in boiling water 10 minutes. Let cool and separate the leaves.
Heat the oil in a frypan and saute the onion, carrot and leek until softened. Add the breadcrumbs, egg, parsley and sour cream. Season with salt and pepper. Divide the filling between the cabbage leaves and roll up, tucking in the ends.
Place the rolls in a saucepan and add vegetable stock just so the rolls are covered. Bring to a simmer and cook 10 minutes.
Place the rolls on a heated plate to serve. Add the cream and tomato paste to the sauce and mix in, then pour over the rolls.