400g piece beef fillet
2 tbsp olive oil
leaves from 1 rosemary sprig, bruised
1 garlic clove , crushed
2 tbsp butter
200g mixed wild mushrooms
200ml good beef stock
1 tsp balsamic vinegar , to serve
Rub the beef with 1 tbsp oil, rosemary and garlic, then leave in the fridge for at least 1 hr, or up to 24 hrs. Make sure the beef returns to room temperature before you cook it.
Heat oven to 200C/fan 180C/gas 6. Heat a non-stick, ovenproof frying pan or roasting tin until very hot. Rub most of the garlic and rosemary from the beef, season with black pepper and flaky salt, then sear on all sides until dark brown and almost crusted – about 5 mins in total. Transfer the pan to the oven, then roast the beef for 10 mins for mediumrare. Leave to rest for a good 15 mins and keep any juices.
While the meat rests, sauté the mushrooms. Heat 1 tbsp butter and the remaining oil in a large frying pan, then tip in the mushrooms with plenty of seasoning. Fry until golden and just softened, then tip into a bowl.
Add the stock to the mushroom pan, then reduce by two-thirds. Tip in the mushrooms and balsamic, then add the remaining butter and let it melt. Tip in any meat juices, then season to taste and keep warm. Thickly slice the beef and spoon over the sauce. Serve with mash and spinach.