Steps

• In a large skillet over medium heat, add olive oil. Sauté chopped onions until they become translucent, then add garlic. Allow it to become fragrant before stirring in the chopped mushrooms and thyme. Cook until the mushrooms have released their liquids and it has evaporated. Season with salt and pepper. Set mixture aside to cool.
• In a mixing bowl, combine ground beef, Worcestershire sauce, and Dijon mustard. Mix until well incorporated. Once the mushroom mixture has cooled, fold it into the ground beef. This combination will form the flavorful core of your Wellington.
• Lay out a large piece of plastic wrap on your counter. Spread the beef mixture onto it, shaping into a log. Ensure it's compact to hold the shape. Wrap the plastic tightly around the log and chill in the refrigerator for at least 30 minutes. This step helps macerate flavors and maintain the shape for baking.
• Preheat the oven to 400°F (200°C). On a floured surface, gently roll out the puff pastry to a size that will comfortably wrap around the beef mixture. Place the chilled beef log onto the pastry. Carefully remove the plastic wrap.
• Brush the edges of the puff pastry with beaten egg. Roll the pastry over the beef log, ensuring snug wrapping, then press to seal. Tuck in the sides and seal the edges with more egg wash.
• Transfer the wrapped log onto a baking tray, seam side down. Brush the surface with remaining egg wash for a glossy finish. Make shallow slits on top for steam to escape. Bake in the preheated oven until golden brown, approximately 25 to 30 minutes.