Preheat your oven to 400 degrees Fahrenheit.
Pat the beef tenderloin dry with paper towels. This is key for a nice sear.
Season the beef generously with kosher salt and black pepper on all sides.
Rub it to adhere the seasoning.
Heat olive oil in a large ovenproof skillet over medium-high heat until it starts to shimmer.
Add the beef and sear it for about 3 minutes on each side until you get a rich, brown crust.
Transfer the skillet to the oven.
Roast the beef for about 25-30 minutes.
Use a meat thermometer to confirm the desired doneness — aim for about 135 degrees Fahrenheit for medium-rare.
While the beef roasts, combine the red wine, chopped rosemary, minced garlic, and butter in a small saucepan over medium heat.
Cook until the butter melts and the mixture is aromatic.
Serve drizzled over the beef slices.