For the bistecca alla fiorentina, mix the olive oil with rosemary and crushed garlic and marinate the steaks in it for at least 24 hours (turning occasionally). Lift out steaks and grill on a well-heated charcoal grill for about 4 minutes on each side.
Meanwhile, brush repeatedly with the marinade. Remove from grill and let rest while still warm for 5 minutes. Only immediately before serving, salt and pepper the bistecca alla fiorentina. Serve and carve at the table.