1. Season the piece of beef thoroughly on both sides.
2. To a hot pan, add some of the butter and some olive oil.
3. When the oil is hot place the steak in the pan and don't move it for a couple of minutes (depending on thickness and preference of doneness).
4. Turn the meat once it's cooked on one side and cook the other side for the same amount of time. Remove from the pan to rest.
5. Finely chop the onion very finely in a food processor or chopper. In the steak pan throw in some more butter and add the finely chopped shallots, thyme sprigs and the chopped mushrooms.
6. Scrape the pan and stir to stop it catching.
7. Add the Madeira and flame the mixture. Once the flame dies down add the beef stock and the Worcestershire Sauce. Reduce with any resting juices from the beef.
8. Add the double cream and bring to the boil. Season with salt and pepper.
9. Serve the steak, with a generous serving of sauce and sprinkle over the chives.