Cooking Method-
First, get that oven cranked up to 400 degrees Fahrenheit or 200 degrees Celsius. Then, it's time to prep the beef. Season it really well with salt and pepper, and sear it in a hot pan with a little bit of oil to get a nice crust. Let it cool down a bit before you move on.
While the beef's resting, make the mushroom mixture. Saute the shallots and garlic in butter until softened, then add the chopped mushrooms and thyme. Cook until the mushrooms release their liquid and it all gets a bit golden brown. Stir in the brandy or cognac and let it bubble a bit to burn off the alcohol. Season that mixture with salt and pepper.
Now it's time to assemble. Spread the mushroom mixture onto a sheet of puff pastry. Put a thin layer of Dijon mustard on the seared beef, then place it on top of the mushrooms. Wrap it up tight in the puff pastry, making sure it's sealed well. Brush the top with the beaten egg – that gives it a nice shine.
Bake the Wellington for about 30-35 minutes, or until the pastry is golden brown and the internal temperature of the beef is around 130 degrees Fahrenheit or 55 degrees Celsius for medium-rare. Let it rest for a few minutes before slicing and serving.
You can add some veggies on the side, maybe some roasted asparagus or some caramelized carrots. And if you want to go all out, a little red wine sauce on the side is always a nice touch. And Enjoy