The steak is cut from the loin, just below the rib cage and above the round or rump (depending on which side of the pond you come from!).
Traditionally the meat for a Bistecca alla Fiorentina comes from a Tuscan breed of cattle called the Chianina, and whilst that is often still the case, several other breeds are used, too. The most important factor by far is the period that the beef is left to hang before being butchered. For a good Bistecca alla Fiorentina that should be between 15 and 21 days (compared to the 48 hours allowed for much of our supermarket meat). Cooking a Bistecca alla Fiorentina is definitely an art. The steak should always be cooked from room temperature and never from the fridge. A high temperature is required and the steak is cooked for just 3–5 minutes on each side, turning it once, with no condiments. The outside of the steak should be almost charred, with distinct grill lines from having been over live charcoal coals (no gas or electric hobs will do here!) and the inside will be very rare and only warm, certainly not piping hot. Just a light shower of salt before serving is perfect. Pepper, olive oil and other things are generally signs of a less than perfect steak.
If you are not happy with a very rare steak, it’s probably best not to order a Bistecca alla Fiorentina. In order to get the inside well cooked, the outside will be as tough as old boots and possibly crunchy, too!