Fontina and Spinach Stuffed Beef Tenderloin

1. Preheat your oven to 400°F (200°C). 2. Cut a slit lengthwise down the center of the beef tenderloin, being careful not to cut all the way through. 3. Stuff the tenderloin with spinach and fontina cheese. 4. Rub the outside of the beef with olive oil, salt, and pepper. 5. Place the stuffed tenderloin on a baking sheet and roast in the preheated oven for 25-30 minutes, or until it reaches your desired level of doneness. 6. Let the beef rest for a few minutes before slicing and serving.