Prepare the Tenderloin: Preheat your oven to 425°F (220°C). Let the beef tenderloin sit at room temperature for 30-60 minutes. Pat it dry with paper towels. Tie the tenderloin with kitchen twine at 1.5-inch intervals to create a uniform shape. Rub the entire surface with olive oil, then season generously with kosher salt and black pepper.
Sear the Beef: Heat a large, oven-safe skillet (cast iron is ideal) over medium-high heat. Once hot, carefully place the tenderloin in the skillet. Sear for 2-3 minutes per side, until a deep golden-brown crust forms all around. This step is key for developing flavor.
Make the Cranberry Glaze: While the beef sears, combine all glaze ingredients (cranberry sauce, balsamic vinegar, brown sugar, Dijon mustard, minced garlic, rosemary, and thyme) in a small saucepan. Bring to a simmer over medium heat, stirring occasionally. Reduce heat to low and let it gently simmer for 5-7 minutes, until it has thickened slightly. Remove from heat and set aside.
Roast and Glaze the Tenderloin: Transfer the skillet with the seared tenderloin directly into the preheated oven. Roast for 20 minutes. After 20 minutes, brush a generous layer of the cranberry glaze over the top and sides of the tenderloin. Continue roasting for another 10-15 minutes, or until an instant-read thermometer inserted into the thickest part reads 130-135°F for medium-rare.
Rest, Slice, and Serve: Carefully remove the tenderloin from the oven and transfer it to a cutting board. Tent it loosely with foil and let it rest for 15-20 minutes. This is a critical step for a juicy roast. After resting, remove the twine and slice the tenderloin into 1-inch thick medallions. Serve immediately with any remaining glaze spooned over the top.