Beef sirloin with king oyster mushrooms

Method

1. Put the beef in a large stainless steel, glass or ceramic bowl, pour over the wine to cover and add the thyme, shallots, peppercorns and garlic. Cover with cling film and marinate in the fridge for 6-12 hours, turning a few times.
2. Drain the beef, setting aside the solids and wine separately. Pat the beef dry and set aside (not in the fridge – it needs to be at room temperature when you cook it).
3. Heat a large heavy-based saucepan over a medium heat and add a glug of oil and the butter. When it foams, add the beef trimmings, if using, and reserved thyme, shallots, garlic and peppercorns. Brown for a few minutes, then pour in the reserved wine and cook for 20 minutes or until reduced by three quarters. Add the 2 stocks and bring to the boil, uncovered. Using a spoon, skim off any foamy impurities that rise to the surface, then reduce for an hour, stirring occasionally, until you have a rich sauce. Pass through a sieve and discard the solids. Season the sauce and set aside in a pan.
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4. For the mushrooms, heat a large griddle pan over a medium heat. In a small pan, melt the butter along with the garlic. Drizzle a little oil over the mushrooms, then season and cook in the griddle pan, brushing with some of the garlic butter, for 3 minutes on each side or until browned. Brush with the remaining garlic butter, then put the mushrooms on a plate and keep warm in a low oven.
5. Cook the potatoes in a large pan of simmering salted water for 15 minutes or until just tender. Drain well and put in a stand mixer fitted with a paddle attachment (or put in a large mixing bowl and use an electric hand mixer). Mix on a medium speed until smooth. Mix in the cream and cubed butter, then slowly drizzle in the oil (the mix will be very rich and soft). Season, then keep warm in a medium pan.
6. Heat the griddle pan over a high heat and the oven to 200°C/180°C fan/gas 6. Season the beef well. Sear on all sides, then transfer to the oven and cook for 25 minutes or until medium rare (a digital probe thermometer pushed into the middle should read 55-60°C). Transfer to a board, loosely cover with foil and rest for 10 minutes.
7. Bring the sauce to the boil, then simmer and add the bone marrow. Cut the beef into thick slices and serve with the mushrooms and sauce and the mash on the side.