1. Prepare the Beef Tenderloin

• Trim the tenderloin: Remove excess fat and silver skin using a sharp knife.
• Butterfly the meat: Slice the tenderloin lengthwise down the center, but don’t cut all the way through. Open it like a book.
• Flatten gently: Use a meat mallet or rolling pin to even out the thickness to about ½ inch.

2. Make the Stuffing

• Heat olive oil in a skillet over medium heat. Add shallots and garlic, sautéing for 1-2 minutes until fragrant.
• Add mushrooms and cook until softened, about 4 minutes.
• Stir in spinach, cooking until wilted. Remove from heat.
• Mix in Parmesan cheese, breadcrumbs, thyme, and rosemary. Season with red pepper flakes (if using). Let cool slightly.

3. Stuff and Roll the Tenderloin

• Spread the stuffing evenly over the butterflied tenderloin, leaving a ½-inch border around the edges.
• Carefully roll the tenderloin tightly from one long side to the other.
• Secure the roll by tying it with butcher’s twine at 1-inch intervals.

4. Season and Sear the Meat

• Rub the outside of the roast with olive oil, salt, black pepper, garlic powder, and paprika.
• Heat a cast-iron skillet or ovenproof pan over medium-high heat.
• Sear the beef on all sides for 2 minutes per side to develop a crust.

5. Roast the Tenderloin

• Preheat oven to 400°F (200°C).
• Brush the roast with melted butter or Dijon mustard for extra flavor.
• Place in the oven and roast for 35-45 minutes, basting with beef broth halfway through.
• Check for doneness with a meat thermometer:
  • Rare: 120°F
  • Medium-rare: 130-135°F
  • Medium: 140-145°F
  • Well-done: 150°F+

6. Rest and Slice

• Remove from oven, tent with foil, and let rest for 10 minutes before slicing into medallions.