Pick out the larger mushrooms and put them in the hot stock. Leave to soak for 20 minutes until soft. Very finely chop the remaining mushrooms (to make 1 tablespoon). Using a blender or pestle and mortar, blend all of the mushrooms, thyme, garlic and 1 tablespoon oil to a smooth paste. Season well.
Pat the meat dry with kitchen paper. Using a small sharp knife, cut about 10 slits all over the beef. Use your fingers to push a little of the paste into each slit. Then put in the fridge to marinate for a couple of hours or overnight.
Preheat the oven to gas 7, 220°C, fan 200°C. Rub 1 tablespoon oil over the beef and season. Put on a baking tray and cook for 25 minutes. Reduce the heat to gas 3, 170°C, fan 150°C and cook for 15 minutes per 500g (1lb) for rare, 20 minutes for medium.
Heat 1 tablespoon oil in a pan and cook the shallots for 5 minutes until softened. Stir in the flour and cook for 1 minute. Add the wine and bubble until reduced by half. Add the porcini mushrooms and their soaking liquid (holding back the grit at the bottom). Simmer for 5-10 minutes until slightly thickened.
When the beef is ready, remove from oven, cover with foil and leave to rest for 15 minutes. Skim off excess fat from the roasting tin, then add 3 tablespoons of boiling water and scrape up all the caramelised roasting juices. Add this to the warm gravy, along with the juices from the rested beef. Carve the beef into slices and serve with gravy.
Seemore Beef recipes
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