Broccoli Cheddar Soup

This recipe is from the Joy of Cooking: All About Vegetarian Cooking
3 tablespoons unsalted butter
1 cup onion, chopped
1/2 cup celery, chopped
4 cups broccoli florets, chopped coarsely
1/3 cup all purpose flour
4 cups vegetable broth
2 cups milk
2 cups grated cheddar cheese
1 teaspoon prepared Dijon mustard
1/4 teaspoon freshly grated black pepper
salt to taste

1. In a large soup pan, melt the butter over medium heat and add the onion, celery, and broccoli, stirring until tender, about 5 minutes. Then sprinkle the flour of the top and stir well to blend. Continue to stir constantly until the flour is cooked without burning it, about 3 minutes.
2. Gradually add in the broth and milk, stir until smooth. Cook until the vegetables are tender, about 8 to 10 minutes.
3. Transfer to a food processor or blender and puree in batched until smooth. Return the soup to the pot and return to a very low simmer. Stir in the cheese in batches, allowing each batch to melt before adding more. Do not allow the soup to boil or the cheese will break down.
4. Add the Dijon mustard, pepper and salt to taste prior to serving. Enjoy.