First make the mushroom mixture which can be made a day in advance.
Melt butter in fry pan add onion, saute until soft add chopped mushrooms cook until moisture has evaporated, then add the cream stir over a low heat until thickened.Add parsley and season with salt and pepper. This part of the dish can now be set aside,if making it a day ahead store in fridge until ready to use.
To prepare the beef heat olive oil in a fry pan when the pan is hot add the beef and sear all sides until browned. Remove from heat put on a plate and set aside to cool.
While the beef is cooling lightly flour a surface and roll out the puff pastry big enough to envelope the beef. Take two pancakes and lay them on top of the pastry, next spread the fois gras onto the centre of the pancakes enough that it will cover the top and sides of the fillet. (allow fois gras to come to room temperature as this will make it soft and easy to spread) Then spread the mushroom mixture on, the same as the fois gras take the beef and place on top of the mushroom mix press down gently. Take remaining two pancakes place on top of fillet.Wrap the pastry around the fillet and fold in sides to envelope beef,and seal with beaten egg.
Turn over and place seam side down on buttered baking tray. You can decorate the top with cut out pastry leaves if you want. The wellington has to be refrigerated now for one hour before baking.
To cook preheat oven to 190°C and bake beef until pastry is golden brown approx 35-45 mins, a little longer if you prefer your beef more well done. Remove from oven and stand for 10mins before serving.
Preparing the madeira truffle sauce.
Bring broth and madeira to boil then turn down heat and simmer until reduced by half. Mix cornflour with water to form a paste and add just to thicken slightly, add truffles allow to simmer a few minutes more then add butter and serve immediately.
It sounds complex but it really is not and it is well worth it for a special occasion. Most of it can be prepared in advance so you can enjoy time with your guests while it is cooking.