Preheat a skillet over medium heat.
Sear the beef on all sides, 3 to 4 minutes. Remove from skillet, cover with foil and rest.
Mince the mushrooms and season with the 1 teaspoon Tony Chachere’s.
In the same pan you seared the beef, melt the butter.
Sauté the mushrooms, minced shallot, and thyme.
As you are cooking, the liquid will render from the mushrooms, making the pan a bit wet. Continue to cook until all the liquid has dissolved and the pan is dry, about 15-20 minutes, stirring often.
Remove the mushroom mix from the pan and allow to cool.
Arrange the parma ham over plastic wrap on a clean work surface.
Cover the ham with the cooled mushroom mixture.
Combine the mustard and remaining Tony Chachere’s. Coat the tenderloin in the mustard mix.
Arrange the tenderloin on one edge of the ham and mushroom layer and roll tightly, using the plastic wrap to help you handle the meat as it rolls.
Wrap and chill 20 minutes.
Meanwhile, whisk the egg with 1 tbsp water and set aside.
On a clean, lightly floured surface, roll the puff pastry out to a ¼ in thick, and approximately 2 inches longer on all sides than the tenderloin. A 10 x 12 square should be sufficient depending on the size of the tenderloin.
Carefully, unwrap the tenderloin from the plastic wrap and start on the dry edge of the puff pastry, roll the beef and puff pastry to coat the tenderloin, pinching the edges to secure.
Place the seam on the bottom and fold the edges under.
Wrap and allow to chill another 20 minutes.
Preheat the oven to 425.
When ready to cook, brush the puff pastry with the remaining egg wash, and slice several vents gently across the top to allow steam to escape.
Bake for 40 to 45 minutes, until an instant-read thermometer reads 130 and the pastry is golden and flaky.
Allow to rest 10 minutes before slicing.
Heat the pan the mushrooms were sautéd in over medium-high heat. Add the beef trimmings and cook until browned all over.
Add the thyme, garlic, black peppercorns, mustard and Tony Chachere’s and stir to coat the pan.
Whisk in the brandy, scraping up any browned bits as needed.
Slowly whisk in the beef stock and allow to simmer for 20 minutes. Remove the beef.
Remove from heat and stir in the heavy cream.
Serve the sliced Beef Wellington with desired sides and a drizzle of brandy cream sauce.
Garnish with fresh parsley and thyme.