COOK IT.
First, preheat your pellet smoker to 250°F. While it is preheating, start prepping your filet mignon roast. Remove any silver skin or hard fat that might surround your filet mignon part of the beef tenderloin.
Next, bind your chateaubriand with an olive oil binder by rubbing 1 Tbsp oil on all sides evenly. This will help your seasoning adhere to the filet mignon roast. Next season your beef with either equal parts salt/pepper/garlic powder.
For this Chateaubriand recipe, we are going to do a reverse sear method to get next to zero gradients and evenly cooked to perfection. What is reverse sear? It is the process of slow cooking a piece of meat and then searing it at the end of the cooking process.
Once your grill is up to temperature, place your filet mignon roast directly on the grill for 1.5-2 hours. You want to cook your chateaubriand no more than "medium". I highly suggest keeping an eye out on the temperature and once it reaches an internal of 110°F, move it aside, turn up the grill temperature to 500°F, open your sear plate, and sear all sides for a minute or two. This should bring your roast up to a perfect internal temperature of 114°F.
The final step is the most delicate part of creating Chateaubriand for two. Cutting the two most inner pieces of your filet mignon, discarding the outer portions, and enjoying that beautifully tender delicate chateaubriand. Cut across the grain into 2" slices.