Preheat your oven to 450 F (230 C). Take a 2.5 lb. beef fillet steak and rub it with 1/4 cup of butter and freshly ground black pepper to taste.

Bake this in the preheated oven at 450 F (230 C) for about 20 minutes, or until a meat thermometer reads 120 F (50 C) in the thickest part.

While beef fillet is cooking, prepare the mushroom duxelles: take a large skillet, heat over low heat, melt 1/2 a cup of butter. Once the butter is melted, add in 2 minced shallots, and cook for about 5 minutes, until they are translucent.

Then add in 1 lb. of white button mushrooms, minced, add an additional 2 tbsp of butter and 1 tsp of salt. Cook this very slowly, stirring occasionally, to dehydrate the mushrooms completely. These will take about an hour, until the mushrooms are dark. Let this cool to room temperature.

While the mushrooms are slowly getting cooked / dehydrated, the beef in the oven will reach 120 F (50 C). Take it out of the oven and place it on a rack. flame it with 1/3 cup of cognac, and salt to taste. Set this aside and let it cool to room temperature.

When both the beef fillet and the mushroom duxelles are cooled to room temperature, measure the circumference of the fillet, and roll out the push pastry (defrosted according to packet instructions) according to fillet circumference, so that the puff pastry will cover the fillet completely, and overlap at the ends and at the bottom. Trim off any excess pastry, and reserve extra pastry for decorations. Preheat oven to 425 F (220 C)

Brush fillet with a layer of foie gras (about 2-3 oz of foie gras). Then on a flat surface, place a layer of plastic cling wrap, then the puff pastry on top, then spread a layer of the room temperature duxelles on top of the puff pastry.

Place the foie-gras-smothered fillet in the middle. Bring the edges of the pastry together and seal with egg white from 1 egg. Twist the ends together to make sure the fillet is completely sealed in the pastry.

Bring the edges of the plastic cling wrap together and twist it to squeeze the roll and create a uniform cylindrical shape. When you're happy with the shape of the roll, remove the plastic cling wrap.

Optional step: use excess pastry to make decorations (e.g. leaves, etc.) and place them on top of the roll.

Take the remaining egg yolk and beat it with 1/4 cup of heavy cream. Brush the pastry with this mixture, to give it a nice golden-brown finish when it bakes.

Bake this in the oven at 425 F (220 C) for 10 minutes, then reduce the heat to 375 F (190 C) for another 20 minutes, or until the crust looks golden brown.

Take it out of the oven and let it rest for 10 to 15 minutes before transferring onto a serving dish. Carve using a serrated knife, each slice about 3/4 inches thick. Enjoy!