Bring it to room temperature: Take the steak out of the fridge 20 minutes before cooking and pat it dry, as a cold steak cooks unevenly. Heat the oven to 180°C (350°F).
Season well: Rub the steak all over with the oil, then season generously with salt and pepper on both sides and the fatty edge.
Sear the crust: Get a large pan smoking hot. Sear the tomahawk until deeply golden, a few minutes each side, holding the fatty edge down too. Add the butter, garlic and thyme and baste for a minute if you like.
Finish in the oven: Transfer to a baking tray and cook for 24 minutes, turning once after 12, for medium rare.
Check it: Pull it at 54 to 57°C in the centre, away from the bone. It climbs a few degrees as it rests.
Rest properly: Rest for 10 minutes, loosely covered. With a steak this size, this is not the step to skip.
Carve and serve: Slice the meat off the bone, then cut across the grain into thick strips. Serve on a board with English mustard.
