1. Melt butter or margarine in large saucepan, add celery and onion; cook until transparent. Add potatoes and 1/2 cup water. Bring to a boil. Cover and simmer until potatoes are tender, about 10-15 minutes.
2. Combine flour with some of the milk and add to potato mixture stirring until thickened and smooth. Add ham and remaining 3-4 cups of milk gradually, stirring constantly. Use low heat. Add seasonings and garnish with chopped parsley.