Wash mussels and them boil. Once cooked remove the shells. Fry with olive oil finely chopped onion, add the chopped celery root, peeled and chopped tomatoes, crushed garlic, pepper and salt and stew for 5 minutes. Pour the white wine and boil until thickened. Then add the mussels, little water and mix well. Serve with lots of lemon and chopped parsley.