In a 3 litre soup pot, saute onion in 1 tbs of butter. Add carrot and potato; stir in water, tomato paste, thyme and bay leaves. Bring to a boil; reduce heat and simmer until potato and carrot are cooked, about 20 minutes. Add more water if necessary to keep vegetables covered. Toward the end of the cooking time, add wine, beans, garlic and salt. Return to the boil; lower heat and simmer uncovered, 10 minutes more. Remove bay leaves and discard. Meanwhile, saute mushrooms over low heat in the remaining tbs of butter. Combine with the beans mixture and serve. Perfect with a wedge of crusty bread.