Turn the slow cooker on to high or low. Put all of the vegetables, bay leaves, thyme and pearl barley into the slow cooker dish. Mix the tomato purée into the hot stock and pour over the vegetables. Mix well and cover with a lid. Cook for 4 hours on high or 8 hours on low.
Remove the bay leaves and thyme stalk then stir in the butter and chopped parsley. Add seasoning to taste and serve hot.
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