Finely chop the mushrooms, shallots and garlic. Alternatively, you could use a food processor to dice them – just make sure you do it individually and not combine them in the processor.
Place the shallot and garlic in a pan on medium heat with 1 tbsp butter. Allow them to become translucent.
Once translucent, add the mushrooms and season with salt and black pepper. Allow the mushrooms to steam off excess water then slowly incorporate the wine/sherry; about 2 tablespoons at a time. Cook until the liquid has evaporated. If the liquid isn’t evaporated enough, you will end up with a soggy pastry.
Let the mixture continue to dry and brown as much as possible. I recommend letting it stay in the pan until ready to use. This isn’t an exact science but it’s one of the most important parts to your success. You want to have a paste when you are complete.
Next, use the butcher’s twine on your beef tenderloin in four places to make it as cylindrical as possible. This will allow for even cooking throughout.
Note: If the tenderloin is not equal in diameter from beginning to end you can ask your butcher for the center cut (also referred to as the chateaubriand). This will give you the most consistent cooking time and temperature.
Liberally apply a coat of olive oil on the tenderloin and season generously with salt and pepper on all sides. Allow the meat to sit at room temperature….it’s almost impossible to get a good sear if the pan has to try to heat a cold cut of beef.
Heat a heavy skillet, such as a cast iron, on high. You’ll want to see steam rising from the skillet.
Place the tenderloin in the skillet and sear it on all six sides for about 1.5-2 minutes per side until it forms a crust. Remember you are not cooking the meat. You want the inside to remain raw. Note-Use tongs or a kitchen towel to maneuver the meat around the pan. Take advantage of the sides on the pan by pushing the tenderloin against them to brown. This will help save a little time and ensure it is seared at all points.
Once the crust is complete and the tenderloin is still hot brush with horseradish. I’m not kidding! There’s something special about the marriage between horseradish and beef. The tangy and spiciness really accentuates the light beefy flavor of a tenderloin. If you don’t like the bite of horseradish substitute with a good Dijon. Once it is coated allow the meat to rest at room temperature.
Place one large sheet of plastic wrap down. You’ll want enough so that you’re able to wrap the entire beef tenderloin. Having too much isn’t a big deal but let’s be gentle on the environment.
Overlap 8 slices of prosciutto to form a large square – large enough to cover the tenderloin. Leave an inch at the end so that you will have something to grab when we get to the rolling part.
A note about the prosciutto - it’s important to ask the deli specifically for prosciutto at a medium thickness so that it doesn’t tear apart. Have them add wax paper between each slice.
Use a spatulate or the back of a spoon to apply an even layer of the duxelles (mushroom mixture).
Sprinkle with fresh thyme. If you have spent enough to buy the tenderloin, fresh thyme is the best way to go. However, in a pinch you can substitute dried thyme, just reduce the amount of thyme by half.
Now it’s time to do the first of two rolls: Place the coated tenderloin on your duxelles and prosciutto blankets and wrap from the bottom of the plastic. The tighter the better, while keeping it in a cylinder and uniform. Twist at the ends. Think tootsie pop meets burrito.
Now place this precious meat burrito in the refrigerator for 30 minutes. If you haven’t already done so thaw out the frozen puff pastry.
Lightly sprinkle flour on your surface to prevent the thawed puff pastry from sticking. Lay your pastry flat and after 30 minutes has passed for your beef, roll it up in the pastry. Just like we did with the prosciutto, roll the puff pastry until the edges meet then trim any excess pastry. Pinch the sides so that it is fully encased.
Preheat your oven to 400° for convection or 425° for regular/conventional.
While the oven is preheating crack two eggs and discard the whites (or save for an omelet). Mix with 1 tbsp of water and brush over the pastry. The more egg mixture you brush the darker it will be so try to coat evenly. If you want to really wow everyone with your presentation take an extra sheet of puff pastry and cut it with a lattice pastry cutter. Set this on top of the pastry and finish by lightly brushing with the egg wash. Too much will create eggy pockets and you don’t want those.
Place in the oven until golden brown. This is for medium rare but if you like it cooked more lightly tent aluminum foil and probe until the desired temperature is achieved.
Allow beef wellington to rest for 10 minutes before slicing and enjoy!