- Place the Chateaubriand on a cutting board long ends on the sides. Begin to lightly slice into the beef long ways turning the beef a quarter turn, and then slice a little more. Keep doing this until you have a uniformly flat piece of beef about ½ inch think. Season the meat with salt and pepper
- Saute the spinach in 2 tbsp of butter just until wilted set aside.
- Mix together the remaining butter, fontina, hazelnuts, cream cheese, lemon juice, sage, and cooled spinach. Taste mixture and adjust seasoning with salt and pepper.
- Spread mixture on rolled out Chateaubriand . Roll the beef back up, and truss. Season the outside with salt and pepper.
- Roast in a 400 degree oven until desired doneness is achieved. About 30 minutes for medium rare or 130 degrees internal temperature.
- Pull out of the oven and let rest for 5-10 minutes before slicing, and serving.