Sour Cream Potato Soup

• 1 salt and pepper
• 475 ml milk scalded
• 450 gr potatoes (diced raw)
• 475 ml chicken broth
• 240 ml sour cream
• 240 ml water
• 60 gr onion (chopped)
• 50 gr celery (chopped)
• 45 gr butter
• 8 gr flour