Put butter in a heated, deep saucepan, add in bay leaf and onion and fry for 1 - 2 minutes until fragrant and onion turns soft.
Add in button mushrooms, carrot, tomato and tomato sauce. Continue to fry for 2 - 3 minutes.
Add fresh chicken stock and bring to the boil. Reduce the heat and simmer for 8 - 10 minutes then add in cabbage and cook for an extra 1 minute. Mix in flour paste and stir vigorously to thicken the soup. Season to taste.