About 45 minutes before you want to cook your steak, pat it dry using paper towel, then season well with salt. Preheat the oven to 200˚C.
For the miso butter mash, cut the garlic bulb in half widthways. Place each half on a square of foil large enough to enclose, drizzle lightly with olive oil, then wrap tightly. Bake for 30 minutes or until the garlic is soft and golden. Cool slightly, then squeeze out the garlic from one of the halves; reserve the other half for another use.
Meanwhile, cut the potatoes into 4cm chunks, then cook in a small saucepan of boiling salted water for 20 minutes or until tender. Drain well, then add the roasted garlic, butter, miso and cream. Mash until smooth, season with salt and pepper, and keep warm.
While the potatoes cook, let’s cook the mushrooms using the wet-fry method. Combine the mushrooms in a wok with 125g (½ cup) water, then bring to the boil over high heat. Cook, stirring occasionally, for about 15 minutes or until all the liquid has evaporated. Add the olive oil, reduce the heat to medium-high, then cook the mushrooms for 5 minutes, tossing the wok often, or until golden. Season with salt and pepper and keep warm.
To cook the steaks, first pat them dry using paper towel. Lightly season again with salt. Heat your steak pan over medium-high heat, then add the vegetable oil. Once the oil is hot, carefully add the steaks. Cook for 1 minute, then turn and cook on the other side for another minute. Continue in this way, cooking and turning each minute, for a total of 6-8 minutes, or until the centre of the steaks are 60°C on a meat thermometer (for medium rare). Remove the steaks from the pan and rest for 5 minutes. Serve with the miso butter mash, mushrooms and sprigs of watercress.