Prepare the Beef:
Take your beef tenderloin and season it with sea salt.
Wrap the beef tightly in plastic wrap and place it in the fridge for 1 hour. This helps it hold a nice shape.
Sear the Beef:
Remove the beef from the plastic wrap.
Heat a pan to high and sear the beef for about 45 seconds on each side.
Brush the beef with Dijon mustard, wrap it again in plastic wrap, and pop it back in the fridge to chill.
Cook the Mushroom Mixture (Duxelles):
In the same pan, melt a little butter over medium heat.
Add the diced shallots and cook for about 2 minutes.
Next, add chopped mushrooms and cook them slowly until they lose all their water—this takes about 45 minutes. Stir often.
Then, add 1 crushed garlic clove, plus the thyme and rosemary. Cook for 5 more minutes.
Take the mixture out of the pan and let it cool.
Make the Crepes:
In a bowl, whisk together 3 tablespoons of flour, 1 egg, 140 ml of milk, ½ teaspoon of salt, and 2 teaspoons of sugar.
Lightly grease a pan with butter, then pour in a small amount of batter. Cook each crepe for about 1½ minutes on each side.
Set your crepes aside.
Wrap in Crepes, Prosciutto, and Mushrooms:
Lay down a sheet of plastic wrap on your counter.
Place the crepes on top, slightly overlapping them.
Arrange slices of prosciutto on top of the crepes.
Spread the mushroom mixture evenly.
Put your chilled beef in the center and roll everything together tightly using the plastic wrap.
Chill the roll again to let it firm up.
Wrap in Puff Pastry:
Place another sheet of plastic wrap on your counter.
Roll out (or lay out) your puff pastry if it’s not already.
Unwrap your beef roll and place it in the center of the pastry.
Brush the edges of the puff pastry with beaten egg (egg wash).
Wrap the pastry around the beef roll, sealing the edges.
Lightly brush the top with more egg for a golden crust.
Bake:
Preheat your oven to 185°C (about 365°F).
Carefully place your wrapped Beef Wellington on a baking sheet.
Bake for about 30–40 minutes, or until the internal temperature reaches between 55°C and 60°C (around 130°F to 140°F).
This gives you a medium-rare to medium doneness.
Let it rest for 30 minutes before slicing.