Heat oven to 200C/180C fan/gas 6. Put an ovenproof griddle pan on a high heat. Season the steak on both sides, then rub both sides with the garlic cloves, thyme and olive oil. Put the steak in the hot pan and char the underside for 2 mins or until griddle lines appear. Turn the steak over to brown the other side, rub the top with the thyme again, then lay the thyme and garlic on top of the meat.
Once evenly browned all over with griddle lines, put the thyme and garlic to one side, hold the steak with a pair of tongs to cook its fatty side and render it down so it’s soft rather than gristly. This will take a few mins. Lay the steak flat again, put the thyme, garlic and butter on top and transfer the pan to the oven to finish cooking for 4-5 mins, until the meat reaches 62-65C on a probe thermometer (or until cooked to your liking).
Rest the meat for 5-6 mins. Serve on a board or large plate in the middle of the table.