Cheese-shrimp Chowder

• 3 potatoes peel
• 1 onion (chopped)
• 475 ml boiling water
• 110 gr process cheddar cheese (shredded)
• 100 gr celery with tops (sliced)
• 60 ml dry sherry
• 1 gr pepper
• 1 package evaporated milk
• 1 package tiny shrimps
• some parsley