Grandpa's Clam Chowder

1 c. finely chopped onion
1 c. finely chopped celery
2 c. finely diced potatoes
2 cans (6 ½ oz.) minced clams (drain clams, save juice)
3/4 c. butter
3/4 c. flour
1 qt. Half and half
1 1/2 tsp salt
dash of pepper

Pour clam juice over vegetables in a small sauce pan, add water to cover and simmer on medium heat until barely tender. Melt butter, add flour, cook until it makes a thick white sauce. Add half and half, stirring with a wisk until smooth and thick. Add rest of ingredients and heat. Season with salt and pepper to taste.