Trim the silver skin and excess fat from the beef tenderloin. Pat dry and season with kosher salt and black pepper. Mince the garlic and chop thyme and rosemary.

Heat the olive oil in a cast iron skillet over medium-high heat. Sear the tenderloin for 3-4 minutes on each side until golden-brown.

Reduce heat to medium and add minced garlic, thyme, rosemary, and unsalted butter. Baste the tenderloin for 2-3 minutes.

Preheat oven to 400°F (200°C). Transfer skillet to oven and roast until internal temperature reaches 125°F for medium-rare, about 15-20 minutes.

Remove from oven, tent with foil, and rest for 10-15 minutes. Slice into 1/2-inch medallions.

Arrange sliced tenderloin on a platter, drizzle with pan juices, and garnish with herbs. Serve with desired sides.