Pan-Seared Sirloin Steak with Garlic-Thyme Butter

Finish. With care pat steak dry with paper towels. Season well on all sides, including edges, using salt and pepper. Let steak rest at room temperature for a period of 45 minutes, or chilled, without sealing covered, up to 3 days (see notes) if wanted. Heat oil over a high flame till only just starting to smoke in a 30 cm heavy-bottomed cast iron skillet. Carefully add steak and cook, flipping often, till a pale golden-brown crust starts to develop, around 4 minutes total. Tip in butter, herbs (if using), plus shallot (if using) to skillet and carry on cooking, flipping steak now and then and basting any light spots using foaming butter. Reduce heat to mid-sized if butter begins in order in order to smoke excessively or steak begins to burn. To baste, tilt pan a little so that butter collects by handle. Use one spoon to pick up butter plus tip it over steak, aiming at light spots. Keep flipping and basting till an instant-read thermometer inserted in thickest part of tenderloin side registers 120 to 50°C (49 to 52°C) for mid-sized-rare or 55°C (54°C) for mid-sized, 8 to 10 minutes total. Promptly move steak to a big heatproof plate and pour pan juices on top. Leave to rest 5 to 10 minutes. Carve and serve.