2Make the duxelles by finely chopping 1 pound (468g) of mushrooms.
3Add 2 finely chopped shallots, 3 finely chopped garlic cloves, and 2 tablespoons (30ml) of olive oil to a cold pan. Sweat the vegetables until translucent.
4Add all the mushrooms and season generously with salt. Continue cooking on medium heat, stirring often, until the mushrooms have released and simmered off the majority of their liquid (about 5-8 minutes).
5Add 3 tablespoons (44ml) of whiskey (optional) and the leaves of 2 sprigs of fresh thyme (also optional) and let it simmer for a minute or two to cook off the alcohol and reduce the liquid until there's almost nothing left.
6Let the duxelles cool off on the side.
7Sear the beef in a pan over medium-high heat with 2 tablespoons (24ml) of high-heat cooking oil like canola oil for about 1.5-2 minutes on each side.
8Place the seared beef on a plate and brush it immediately with dijon mustard while still hot.
9Let the mustard-coated beef cool down to room temperature.
10Make crepes using 3.5 tablespoons (51g) of all-purpose flour, 140 ml of whole milk, 1 egg, and a pinch of salt. Whisk those together and cook in a nonstick pan until golden brown.
11Layer 2-3 crepes so they overlap to create length. Add 6-7 slices of prosciutto to the base of the crepes.
12Spread the duxelles evenly over the prosciutto.
13Gently place the beef at the base of the crepe layer and slowly roll the crepe around the beef until it's completely wrapped.
14Gently roll your wrapped beef in plastic wrap, leaving some excess wrap on the sides, to create tension. Refrigerate to chill and firm up for about 30 minutes to an hour.
15Roll a sheet of puff pastry to an 1/8th of an inch or 1/3 of a centimeter thick.
16Brush the surface of the pastry with egg wash, consisting of 2 egg yolks and 1 tablespoon (14ml) of water.
17Place the Wellington burrito at the base of the pastry, leaving a little lip to grab onto while rolling.
18Slowly roll the puff pastry around the Wellington until the edges meet. Cut off any excess, pinch the edges together to completely close, and cut off any excess on the edges.
19Brush the entire surface of the Wellington with egg wash. Add a lattice pattern on top (optional).
20Sprinkle generously with flaky salt.
21Bake in a preheated oven to 400°F (convection) or 425°F (regular).
22For the metric folks, that's 204°C (convection) or 218°C (regular).
23Bake until golden brown. For medium-rare, check frequently.
24To make a delicious pan sauce, take the chicken stock and reduce it by about 75%, then add a couple tablespoons of unsalted butter and stir until it emulsifies.