Place the filet on a baking dish and season with white pepper, garlic powder, onion powder, fresh cilantro and soy sauce. Roll the fillet around in the mixture so the steak gets evenly coated and absorbs almost all of the liquid.
Place the chateau in the center of a large baking dish. Add enough water so 1/4 inch is standing in the pan. Add the button mushrooms and bake at 400-degrees for about 10 minutes.
Open the oven and turn the fillet over. Let it roast for another 10 minutes. If necessary turn the fillet again. When the fillet starts to bleed and has a140 degree internal temperature (use a thermometer to check), its medium rare and ready to remove from the oven.
Roasting beef tenderloin is a great way to keep it moist and juicy. The liquid in the baking dish will be used as the sauce so don't let it evaporate and dry up completely. Let the fillet sit on the counter to rest while preparing the serving platter.
To serve, pipe mashed sweet potatoes around the border of a platter. Cut the fillet into half inch slices and fan out in the center of the platter. Add the mushrooms to the platter along with the Food Guru's Fried Green Beans. Pour some of the natural roast pan sauce over the steak and serve the rest on the side.