If you prefer, ask your butcher to portion the fillet for you.
Place half of the porcini mushrooms (15g) in small bowl, cover with boiling water and set aside for 5 to 10 minutes or until mushrooms are plump and soft.
To make the compound butter, use a food processor or coffee grinder to grind the dried porcini mushrooms (15g) into a fine powder. Then add the porcini mushroom powder to a bowl with the butter and truffle oil and mix well. Season to taste with salt.
Spoon the butter mixture onto a sheet of cling film and wrap into a sausage shape by folding the plastic wrap over the butter and quickly spinning the two loose ends around.
Refrigerate the porcini and truffle butter until required or put it in the freezer if you need to speed things up.
Drain the water from the bowl of porcini mushrooms and squeeze out any excess water. Thinly slice them and set aside for frying with the fillet.
Prepare the beef fillet by cutting away the silver skin. Carefully slide the tip of a sharp knife under the membrane and move the knife along it at an upward angle pulling the silver skin off of the meat.
Slice off the tail end (keep this as a chef’s snack) and portion the fillet into 4 even pieces just under 250g each. To ensure the steaks cook evenly, tie butcher’s string around each medallion to help keep their shape during cooking.
Coat the fillet steaks in olive oil and generously season with salt and freshly ground black pepper.
Add a splash of olive oil and 2 tablespoons of butter to a smoking hot frying pan and cook the steaks for approximately 4 minutes on both sides for medium-rare. To evenly brown all sides of the fillet, continuously spoon the hot butter from the pan over the steaks whilst cooking; this French technique is called arroser which means ‘to baste’. In the last few minutes of cooking time, add the porcini slices, thyme sprigs and garlic.
Leave the meat to rest for half its cooking time before serving it with a few cooked porcini slices and your choice of side dishes. Unwrap the porcini and truffle compound butter, cut into 1cm thick slices and pop it on top of the fillet medallions before serving.