In a large saucepan, saute onion and celery in butter until tender.
Add potatoes and broth. Bring to a boil. Reduce heat. Cover and simmer for 10-15 minutes or until potatoes are tender.
Puree in small batches in a blender until smooth. Return to the pan.
Stir in the cheese, milk, pepper, and paprika. Cook and stir over low heat until the cheese is melted.
Garnish with croutons.