1. Make the Mushroom Duxelles
2. Heat olive oil in a large skillet over medium-high heat. Add diced mushrooms and season generously with salt, pepper, and thyme. Sauté for about 10 minutes, stirring often, until the mushrooms release their moisture and the pan is dry. The texture should be soft and crumbly. Remove from heat and let cool completely.
3. 2. Prepare the Chive Crêpes
4. In a bowl, whisk together eggs, milk, flour, chives, thyme, and salt until smooth. Chill the batter in the fridge for 30 minutes.
5. Lightly grease a nonstick pan and pour about ¼ cup of batter per crêpe. Swirl quickly to coat the pan thinly. Cook for 25–30 seconds until set, flip, and cook for a few more seconds. Avoid browning. Stack with parchment paper between each crêpe and set aside.

3. Sear the Beef

1. Season the beef tenderloin generously with salt and pepper. Heat grapeseed oil in a cast iron skillet over high heat and sear the meat for 1 minute per side until evenly browned. Remove from the pan, drizzle with the juices, and brush the entire surface with Dijon mustard while warm. Let cool completely.

4. Assemble the Wellington

1. On a clean surface, layer three pieces of plastic wrap. Lay two to three trimmed crêpes vertically to match the beef length. Arrange prosciutto slices evenly on top, then spread the mushroom duxelles in a thin layer.
2. Place the beef at the bottom of the crêpe layer and roll tightly using the plastic wrap. Twist the ends to secure and chill in the refrigerator for 20 minutes to set.

5. Wrap in Puff Pastry

1. Preheat the oven to 425°F (220°C) for convection or 450°F (230°C) for standard bake.
2. Roll out the puff pastry to about ⅛ inch thick on plastic wrap. Unwrap the beef roll and place it ⅓ of the way up the pastry. Brush the edges with egg wash, then roll tightly to enclose the beef. Trim excess pastry and seal the edges.
3. Wrap again in plastic wrap and chill for 10 minutes.

6. Bake the Wellington

1. Remove the plastic, place the Wellington on a parchment-lined tray, and brush with egg wash. Use the back of a knife to score decorative lines across the top. Sprinkle with salt and press a small thyme sprig on top.
2. Bake in the preheated oven for 18–20 minutes, or until golden brown and crisp. Rest for 5 minutes before slicing.

7. Slice and Serve

1. Cut the Wellington into thick slices and serve immediately. The beef should be medium-rare in the center, surrounded by a layer of mushrooms, prosciutto, and flaky pastry.
2. For an elevated touch, pair it with a red wine reduction, roasted vegetables, or creamy mashed potatoes.