"the Postman" Italian Fish Soup

• 1 onion (yellow peeled)
• 1,400 ml fish stock
• 500 gr total of clams
• 240 ml tomato sauce
• 210 gr fillet of fish (white)
• 240 ml dry wine (white)
• 120 ml olive oil
• 100 gr celery (chopped)
• 85 gr mushrooms (fresh sliced)
• 3 slices leeks