A few hours before preparing the dish, remove frozen filo dough and puff pastry from the freezer to allow thawing.

Tie the beef every inch, season it liberally with salt and pepper, and chill it before searing.

Peel and mince the shallots.

Heat the oil in a heavy skillet over medium-high heat until nearly smoking. Sear the tenderloin on all sides in the pan.

Reduce the heat in the pan slightly.

While the beef cools enough to handle, add butter to the pan and melt it, then add the mushrooms to the pan and stir.

Allow the mushrooms to exude their excess water (a lot of liquid will appear in the pan) and cook it out. Allow the mushrooms to start to brown and maybe stick to the pan a little bit. (See picture below.)

Meanwhile, trim the strings from the beef and slather it in mustard. Place it in the refrigerator to cool further.

When the mushrooms are browning, add the shallots and thyme and stir. Cook until the shallots soften somewhat and become well translucent.

Add the brandy to the mushrooms and cook, stirring some, until the brandy is almost completely cooked out.

Add the cream and cook, stirring occasionally, until the cream thickens and the whole mass starts acting like one mass in the pan.

Season to taste with salt and pepper.

Transfer the duxelles to a shallow dish and refrigerate while the loin chills for 30 minutes.

On a wide bed of plastic wrap, lay out the filo dough sheets. If using two smaller ones, lay them out with the long side towards you, overlapping by an inch or two.

Shingle the prosciutto onto the filo dough, leaving a border 2 inches wide along the top and bottom.

Remove duxelles from the refrigerator and stir in the foie gras pâté. Spread onto the prosciutto in an even layer.

Place the tenderloin along the bottom of the ham/shroom layer.

Twist the ends of the wrap tightly like a candy wrapper and tuck them under the package.

Place the roll in the refrigerator.

Dust your work surface with flour and roll out your puff pastry into a rectangle so that it is 4 inches wider than the length of your meat/filo roll. It should be long enough to go all the way around the circumference of your beef.

If using pre-sheeted frozen puff pastry, it may be necessary to glue the edges of two sheets together with a little water. Trim any excess and reserve for decorations.

Place the unwrapped beef roll along the bottom edge of the puff pastry.

Brush the 6 inches of pastry above the beef roll with egg.

Fold the ends of the pastry like you are wrapping a present, but trim the bottom flap off.

Tuck the top flaps under the bottom of the Wellington and return the whole thing to the refrigerator for at least 30 minutes.

Remove the Beef Wellington from the refrigerator and brush with egg.

Add any decorative puff pastry garnishes to the top and sides that you like, then brush them with egg also.

Allow the Beef Wellington to rest for 10 minutes before cutting off the ends and slicing for service.