Preheat your oven: Begin by setting your oven to 400°F (200°C) to allow it to reach the right temperature by the time you're ready to roast the beef.
Prepare the stuffing: In a medium-sized mixing bowl, combine the chopped spinach, softened cream cheese, crumbled feta, minced garlic, minced rosemary, minced thyme, and a generous sprinkle of salt and pepper. Stir the mixture well until all the ingredients are evenly blended, forming a creamy herb stuffing.
Prepare the tenderloin: Take a sharp knife and carefully cut a lengthwise pocket into the center of the beef tenderloin. Ensure you do not cut all the way through the sides, creating a pouch for the stuffing.
Fill the tenderloin: Spoon the prepared herb stuffing into the pocket of the tenderloin, pressing gently to ensure it fills the space evenly without spilling out.
Sear the tenderloin: In an oven-safe skillet, heat the extra virgin olive oil over medium-high heat. Once the oil is shimmering, place the stuffed tenderloin in the skillet. Sear all sides of the beef for about 2-3 minutes per side, or until it develops a nice brown crust.
Add balsamic and roast: Drizzle the balsamic vinegar over the seared tenderloin, enhancing its flavor. Carefully transfer the skillet to your preheated oven and roast the tenderloin for approximately 15-20 minutes, or until it reaches an internal temperature of 145°F (63°C) for a perfect medium-rare.
Rest and serve: Once the beef is cooked to perfection, remove the skillet from the oven and let the tenderloin rest for 5-10 minutes. This allows the juices to redistribute for a more tender slice.
Notes
For a stunning presentation, slice the tenderloin into medallions and garnish with fresh herbs.