Source: dLife

A fillet mignon cooked inside of a puff pastry shell with mushrooms.

Servings

2.5 lb Beef, filet mignon, extra lean, raw
1 pinch black pepper (to taste)
1 Pastry, puff, sheet, baked from frozen dough
1 Eggs, large, raw , beaten with 1 tablespoon water
2 tsp olive oil
2 cup fresh mushrooms , finely chopped
3 medium shallots , finely minced
1 medium garlic cloves , minced
0.25 cup chopped parsley (flat-leaf)
0.5 tsp ground thyme
1 Pastry, puff, sheet, baked from frozen dough (optional)
1 oz fresh thyme , sprigs (optional, or other herbs)

1 Preheat oven to 425 degrees F. Season tenderloin with pepper and place in a lightly greased roasting pan.
2 Roast for 30 minutes, or until an instant meat thermometer reads 130 degrees F. Cover tenderloin with foil and refrigerate for 1 hour.
3 Thaw puff pastry at room temperature for 30 minutes. Reheat oven to 425 degrees F. Beat egg with water and set aside.
4 Meanwhile, heat oil in a heavy skillet over medium-high heat. Throw in the mushrooms, shallots, and garlic.
5 Cook, stirring sporadically, until vegetables are wilted and all liquid has been absorbed. Stir in parsley and thyme. Set aside.
6 Unfold the pastry sheet and place on a lightly floured work surface. Roll out to a rectangle, 4 inches longer and 6 inches wider than the tenderloin. Brush the pastry sheet with some of the egg mixture. Spoon mushroom mixture onto the pastry to within 1 inch of the edges.
7 Place the tenderloin in the center of the mushroom mixture. Fold the pastry over the meat, sealing the ends and edges. Place seam-side down on a heavy baking sheet. If desired, decorate the pastry with small pastry cut-outs, using the remaining egg mixture as your "glue." Bake for 25 minutes, until pastry is golden, and the meat thermometer reads 140 degrees F.
8 Transfer tenderloin to a serving platter and garnish with fresh herbs (if using). Allow to stand for 5 minutes before carving into slices.