Pat the beef tenderloin dry with paper towels.
In a small bowl, mix together the olive oil, salt, black pepper, minced garlic, rosemary, thyme, Dijon mustard, and balsamic vinegar to create a marinade.
Rub the marinade all over the beef tenderloin, ensuring it is evenly coated. Let it sit at room temperature for about 30 minutes.
Heat a large oven-safe skillet over medium-high heat and sear the beef tenderloin on all sides for about 3-4 minutes per side.
Transfer the skillet to the preheated oven and roast for 20-30 minutes, or until the internal temperature reaches 125°F for medium-rare or 135°F for medium.
Remove the skillet from the oven and transfer the beef to a cutting board. Tent it with aluminum foil and let it rest for 10-15 minutes.
Add the butter to the skillet over medium heat and scrape up any browned bits from the bottom.
Slice the beef tenderloin into medallions and serve with the pan sauce drizzled over the top.