Saute the celery-onion-carrot in butter and olive oil until soft. Add the vegetable stock, water and potatoes. The liquid should cover the potatoes. Bring to a boil at lower heat, and add clams and clam juice and cook until potatoes are soft. Add evaporated milk and cheese and heat until the cheese is melted. Season with salt and pepper to taste.
Note: If you want your chowder thickened, used potato flakes a little at a time to thicken to taste.