Filet de Boeuf en Croûte (Beef Fillet in Puff Pastry)

• 700 g Beef filet mignon, centre-cut, tied if needed
• 2 tsp Fine sea salt
• 40 g Unsalted butter
• 2 Shallot, medium
• 350 g Mushrooms
• 6 sprigs Fresh thyme
• 2 tbsp Dijon mustard
• 1 Egg
• 500 g Puff pastry, all-butter preferred

1. Pat the beef dry and season all over with 1 tsp of the fine sea salt. Heat a frying pan over medium-high heat and add 20 g of the unsalted butter. Sear the beef for 2–3 minutes per side until well browned, then transfer to a plate to cool completely.
2. Finely chop the shallots and mushrooms, and pick the thyme leaves from the sprigs. In a saucepan over medium heat, melt the remaining 20 g butter, then cook the shallots with a pinch of the remaining salt for 2 minutes until softened. Add the mushrooms and thyme and cook 12–15 minutes, stirring often, until the mixture is very dry and no moisture remains in the pan.
3. Spread the mushroom mixture on a plate and cool until cold, so it does not melt the pastry. Brush the cooled beef all over with the dijon mustard. Beat the egg in a mixing bowl for the egg wash.
4. On a lightly floured surface, roll the puff pastry into a rectangle large enough to wrap the beef with a little overlap. Spread the cold mushroom mixture in a strip down the centre, set the beef on top, then wrap the pastry tightly around it and seal the seam with a little egg wash. Place seam-side down on a baking tray and brush all over with the remaining egg wash.
5. Chill the wrapped beef for 15 minutes to firm up the pastry. Meanwhile, heat the oven to 200°C (390°F).
6. Bake for 25–30 minutes until the pastry is deep golden and crisp. For medium-rare beef, aim for 52–54°C (125–130°F) in the centre; bake a few minutes longer for medium. Rest for 10 minutes before slicing thickly and serving.

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