Polish Potato Soup-very yummy

This hearty, creamy soup is "the real deal" It's very simple, but has a surprisingly rich flavor.

7 medium potatoes (2 3/4 pounds), peeled and cut into 1- to 1 1/2-inch cubes
3 medium carrots (9 ounces), peeled and thinly sliced
3 celery stalks (3 1/2 ounces), thinly sliced
1 large onion (12 ounces), peeled and chopped
1 1/2 quarts (48 ounces) water
2 cups (16 ounces) broth (chicken, beef or pork)
2 tablespoons (1 ounce) butter
2 tablespoons (1/2 ounce) Unbleached All-Purpose Flour
1/2 teaspoon salt
1/4 teaspoon ground black pepper
1 cup (9 ounces) sour cream or just use an 8-ounce container, if you like.

Place the potatoes, carrots, celery and onion into a large pot. Add the water and broth, and cover the pot with a tight-fitting lid. Cook the soup over medium heat for 30 minutes, or until the vegetables are tender.

Melt the butter in a small saucepan. Stir in the flour, salt, and pepper. Cook the mixture over medium-low heat, stirring constantly, until it bubbles. Add 1/4 cup of the sour cream, stirring till smooth, then add the remaining sour cream and bring the mixture to a boil, stirring constantly. Stir the sour cream into the soup. Bring it to a simmer over medium heat, reduce the heat to low, and simmer for 10 minutes. Serve the soup hot, garnished with chopped parsley, chives, or scallions, if desired.