Recipe(tried): Cream of Celery Soup

From my mother-in-law who passed away in March at the age of 94. She made this at least once a week as long as I can remember.

Cream of Celery Soup

1 1/2 cups celery, chopped
1/3 cup onion, chopped
1 cup water
3 cups milk
3 tablespoons flour
1/8 teaspoon white pepper
2 tablespoons butter

In a 2 quart saucepan, combine celery, onion, 1/2 tsp. salt and water. Cover and cook until vegetables are tender, about 15 minutes. DO NOT DRAIN! Add 2 1/2 cups milk.
Blend remaining milk, flour, pepper & 1/2 tsp. salt. Add to celery mixture. Cook, stirring constantly, until thick and bubbly. Remove from heat. Stir in butter. Season with salt & pepper.