Heat the broth in a 3 qt. saucepan until lightly boiling. Tear the tortillas into short strips. Put some flour in a bag with the tortillas and toss around to coat tortillas. Drop tortilla strips one at a time into the boiling broth, returning to boil after each addition. Return to light boil and boil about 20 minutes (until the tortillas sink into the soup). Add the chicken toward the end. Add a bit of milk right at the end to enrich the broth. Season with a little pepper.