Preheat your oven to 400°F (200°C).
Prepare the stuffing by sautéing the mushrooms and garlic in olive oil.
In a bowl, mix together sautéed mushrooms, spinach, cream cheese, Parmesan, thyme, salt, and pepper.
Butterfly the beef tenderloin and season with salt and pepper.
Spread the stuffing evenly within the beef and roll it tightly.
Tie the rolled tenderloin with kitchen twine to secure the stuffing.
Sear the beef tenderloin in a hot skillet with olive oil until browned on all sides.
Transfer the tenderloin to a roasting pan and pour the beef broth around it.
Roast in the oven for 25-30 minutes, or until internal temperature reaches 130°F for medium-rare.
Allow the tenderloin to rest for 10 minutes before slicing.