Trim any irregular pieces and fat from the filets, saving the trimmings for the red wine sauce. Try to get as uniform a shape as possible so the Wellingtons bake evenly.

Salt the filets generously on all sides and store uncovered in the refrigerator for at least 45 minutes, or up to overnight. The salt draws out moisture that gets reabsorbed, seasoning the meat deeply. The dry fridge air dehydrates the surface, reducing moisture that could make the pastry soggy.

Finely mince the mushrooms using a knife or food processor. Hand-chopping produces slightly irregular pieces that improve texture and flavor.

Heat olive oil in a large nonstick pan over medium-high heat. Add the mushrooms and season with salt. Cook until the mushrooms have given up all their liquid, are lightly caramelized, and have the consistency of dry dirt. This takes 10-20 minutes.

Add the thyme leaves in the last minute of cooking. Adjust seasoning with salt and pepper.

Spread the duxelles on a lined baking sheet and allow to cool completely. Then refrigerate uncovered until totally cold. Store in a covered container for up to 3 days.

Sift the flour and salt into a large bowl. Whisk the eggs until homogenous, then add the milk.

Add one quarter of the egg-milk mixture to the flour at a time, stirring until incorporated after each addition. Run the batter through the strainer to remove any lumps.

Add the chopped chives and thyme leaves and stir until incorporated. Refrigerate the batter for at least 1 hour or up to overnight.

Heat a 10-12 inch nonstick pan over medium-low heat and spray with cooking spray. Add about ¼ cup of batter and swirl to coat the bottom evenly. Cook until the top looks dry, then flip and cook the other side for a few seconds.

Stack the crepes on top of one another, cover, and store in the fridge until ready to use. Crepes can be made the day before.

Heat a pan over medium-high heat and add neutral oil. Remove the filets from the fridge, dry with a paper towel, and immediately sear the cold filets for about 10-15 seconds per side. Do not let them come to room temperature first.

Place the seared filets back into the fridge immediately. The goal is to keep the interior as cold as possible since the real cooking happens during baking.

Dampen your work surface with a wet towel and lay out plastic wrap. Lay enough prosciutto to completely wrap one filet. Spread mushroom duxelles on top of the prosciutto, pressing down to compact it.

Remove the filet from the fridge, dry with a paper towel, and brush with Dijon mustard on all sides. Place the filet flat-side down on the duxelles.

Using the plastic wrap, roll the filet over, pushing in with your fingers and forward with your thumbs. Pinch the sides of the plastic and roll against the table until the mixture forms a tight, uniform log. Refrigerate for at least 20 minutes.

Cut a crepe to slightly wider than the circumference of the filet log. Lay plastic wrap on a dampened surface, place the crepe on top, unwrap the filet, and roll into a crepe-wrapped log using the same technique. Refrigerate for at least 10 minutes.

Dust your surface with flour and lay out the puff pastry. Roll it slightly thinner with a rolling pin, making the seam area thinner than the rest for uniform thickness all around.

Brush the puff pastry with egg wash and sprinkle with salt. Unwrap the crepe-wrapped filet and place it about one-third of the way up from the bottom. Roll up using the plastic, seal and pinch all sides, trim excess, and make sure the Wellington is completely sealed.

Set on parchment paper. Brush the outside completely with egg wash and sprinkle with salt.

Place a baking sheet on the center rack and preheat the oven to 400°F (200°C). The preheated sheet kickstarts the cooking on the bottom for crispier pastry.

Remove the hot baking sheet from the oven. Lift the Wellington onto it using the parchment paper. Bake on the center rack for 20 minutes for medium-rare.

Remove the Wellington from the oven and transfer to a cooling rack. Let it rest for at least 15-20 minutes before slicing. This allows the juices to redistribute instead of leaking onto the cutting board.

Slice and serve with the red wine sauce or Dijon mustard.

Heat neutral oil in a pan over medium heat. Saute the beef trimmings until lightly browned. Add the shallots, peppercorns, bay leaf, and thyme. Saute until the shallots are lightly browned.

Add the red wine vinegar and cook until almost completely dry. Add the red wine and cook until syrupy.

Add the beef stock, bring to a boil, reduce to a simmer, and cook for 30-60 minutes or until desired consistency. Strain, adjust seasoning with salt, and serve immediately or cool and store in the fridge for up to 3 days.