Trim the fillet and remove the chain from the thick side; open the fillet lengthwise along the thick side, stopping short of each end and not cutting completely through. Fill it with thick slices of seasoned raw foie gras, alternating with slices of raw truffle; close it up and stud the top surface with pieces of raw truffle.
Tie fairly tightly with string and place the fillet in a suitable pan lined with slices of raw ham and spread with a cooked Mirepoix. Moisten with sufficient Madeira wine and veal gravy to come halfway up the fillet and braise it, carefully glazing it at the last minute after removing the string.
Place on a long dish and surround with truffles cooked in Madeira and nice mushroom heads cooked in
Serve separately a Sauce Demi-glace containing the braising liquid after first removing any fat, passing through a fine strainer and reducing it by two-thirds.