Beef Wellington with Red Wine Jus

Prepare the Mushroom Duxelles

1. Finely chop the chestnut mushrooms in a food processor until they resemble coarse breadcrumbs.
2. Heat 1 tablespoon of butter and 1 tablespoon of olive oil in a large pan over medium heat. Sauté 2 finely minced shallots and the garlic for 2 minutes.
3. Add the chopped mushrooms and a few thyme leaves. Cook for 15-20 minutes, stirring frequently, until all the moisture has evaporated and you are left with a thick paste (duxelles). Season with salt and pepper, then transfer to a plate to cool completely.

Sear the Beef

1. Pat the beef tenderloin dry with paper towels and season generously with salt and pepper on all sides.
2. Heat 1 tablespoon of olive oil in a hot pan. Sear the beef quickly for 1-2 minutes on all sides (including the ends) just to get a brown crust. Do not cook it through.
3. Remove from the pan, immediately brush all over with the mustard while hot, and let it cool completely on a plate.

Assemble and Wrap

1. Lay a large sheet of plastic wrap (cling film) on a clean work surface. Arrange the prosciutto slices in an overlapping rectangle big enough to wrap the beef.
2. Spread the cooled mushroom duxelles evenly over the prosciutto, leaving a small border at the edges.
3. Place the beef tenderloin in the center. Using the plastic wrap, roll the prosciutto tightly around the beef. Twist the ends of the plastic wrap securely to form a tight, uniform log. Chill in the fridge for 30 minutes to firm up.
4. Dust your workspace lightly with a little flour. Roll out the puff pastry sheet.
5. Unwrap the beef log and place it in the center of the pastry. Roll the pastry around the beef, brushing the edges with some beaten egg to seal the seams. Trim any excess pastry. Wrap the Wellington tightly in plastic wrap again and chill in the fridge for another 30 minutes (or up to 24 hours).

Bake the Wellington

1. Preheat your oven to 200°C (390°F). Line a baking sheet with parchment paper.
2. Unwrap the chilled Wellington and place it on the baking sheet seam-side down. Brush the entire surface with the remaining beaten egg. Use the back of a knife to gently score a decorative pattern on the pastry, being careful not to cut all the way through. Sprinkle with flaky sea salt.
3. Bake for 30 to 35 minutes until the pastry is crisp and golden brown, and the internal temperature of the beef reaches 50-52°C (122-125°F) for medium-rare. Let it rest for 10-15 minutes before slicing.

Make the Red Wine Jus

1. While the Wellington is in the oven, combine the remaining 1 minced shallot, 250ml red wine, and a few sprigs of thyme in a small saucepan over medium heat. Bring to a simmer and reduce the liquid by half.
2. Pour in the 400ml beef fond. Simmer and reduce the sauce until it is thick enough to coat the back of a spoon (about 15 minutes).
3. Strain the sauce through a fine sieve to remove the solids. Return the liquid to the pan, take it off the heat, and whisk in 2 tablespoons of cold butter to create a glossy finish. Season with salt and pepper to taste.
4. Slice the Beef Wellington into thick rounds and serve immediately alongside the warm red wine jus.