Portobella Mushroom Soup

• 5 leeks (white)
• 4 generous
• 3 minut es
• 1 onion (chopped)
• 1 pepper (ground white)
• 1/2 stick
• 700 ml chicken stock
• 100 gr portobella mushrooms (chopped)
• 60 ml dry sherry
• 32 gr all purpose flour