01 - Preheat oven to 425°F.
02 - Pat beef tenderloin dry using paper towels. Secure with kitchen twine at 2 inch intervals for uniform cooking.
03 - Combine black and pink peppercorns, kosher salt, garlic powder, and dried thyme in a small bowl.
04 - Rub tenderloin evenly with olive oil. Coat all sides with prepared peppercorn mixture, pressing gently for adhesion.
05 - Heat a large oven-safe skillet over medium-high heat. Add unsalted butter and rosemary sprigs. Sear beef on all sides, 2–3 minutes per side, until browned.
06 - Transfer skillet to oven. Roast 20–25 minutes, or until thermometer reads 125–130°F for medium-rare.
07 - Remove from oven, loosely tent beef with foil, and let rest for 15 minutes.
08 - Slice tenderloin with a sharp carving knife. Serve drizzled with pan juices.