Jerusalem Artichoke Soup A

• 1 leek only (white)
• 1/2 lemon
• 3,800 ml nonreactive saucepan
• 700 ml chicken stock
• 600 ml stock
• 475 gr jerusalem artichokes
• 120 ml stock
• 120 ml cream (heavy)
• 55 gr butter
• 3 gr salt