Dice coarsely the onion, sauté in the butter until transparency.Cut leek into thine rings, slice carrots and cut into shreds, add in the onion and fry. Slice champignons and add in the vegetables, stew. Pour the boiling water over tomatoes, peel them , chop and add in a pan, bring to a boil. Pour the white wine and bring to a boil again, season with salt, pepper, thyme, basil and broth powder(optional). Wash and peel the mussels. Place into a sauce and boil for 7-10 minutes. Threw away unopened mussels.