Broccoli Cheese Soup

Ingredients:

•  1/2 cup butter
•  1 onion, chopped
•  1 (16 ounce) package frozen chopped broccoli
•  4 (14.5 ounce) cans chicken broth
•  1 (1 pound) loaf processed cheese food, cubed
•  2 cups milk
•  1 tablespoon garlic powder
•  2/3 cup cornstarch
•  1 cup water