Reuben Soup

• 1 1/2 sauerkraut (rinsed)
• 950 ml milk
• 475 ml beef broth
• 475 ml chicken broth
• 250 gr swiss cheese (shredded)
• 120 gr onion (chopped)
• 100 gr celery (chopped)
• 60 ml water
• 55 gr butter
• 32 gr cornstarch