Remove the steak from the refrigerator and allow the meat to come to room temperature, approximately 20 minutes. Pat the meat dry with a kitchen towel which will help to develop a crust when cooking.
Pour the sunflower oil over the steak and season well with salt, then rub the oil into the meat using your hands.
Place a large sauté pan on a high heat and allow it to come up to temperature. Then add the steak to the pan and sear for 2 minutes without moving the meat.
After 2 minutes flip the steak and cook for 2 minutes more on the opposite side. Rare - 1 minute each side, Medium Rare - 1 ½ minutes each side, Medium - 2 minutes each side, Well Done- 4 minutes each side.
A dark crust should have developed on either side of the steak, check the cooking with your finger (firm with a bit of a spring) or a meat thermometer.
Remove the pan from the heat and add the butter, garlic, thyme and rosemary. Baste the butter over the steak then transfer the steak to a plate and pour the contents of the pan over the meat.
Cover the steak with a kitchen towel and allow to rest for 5 minutes.
Once rested, serve the perfectly cooked medium sirloin and season with freshly cracked black pepper.