Guidebook recommends Trattoria al Trebbio. Do not go there. Stale bread, cold appetizers, measly portions. It was obvious that everyone there came because of guidebook and staff could really serve anything. Does not help when American traveler insisted that lasagna should have meatballs with it and also asked for "Japanese sake". I am not kidding and he was serious. Maybe Rick got good meal there, but few others did on night I was there.
Visited Florence in early October '16, found this lovely restaurant, Trattoria 13 Gobbi (translates to 13 Goblins) Via del Porcellana, 9R, Firenze, Italy. the food was brilliant traditional Italian and the staff were exceptional. Being traditional they are not open all day and close mid afternoon and reopen in the evening at 7:30pm.
They are always crowded and booking reservations in advance would be recommended.