Chop onion, carrots, celery, and mince garlic.  In a large soup pot, add the oil and cook the chopped vegetables until tender. Stir in the broth, rice, basil and pepper. Bring to a boil, reduce heat, and cover.  Simmer until rice is cooked.

In a small bowl, combine flour and milk. Whisk until smooth.  Stir into the soup, and return to a boil.  Cook until soup begins to thicken and is hot.