We rarely eat beef but when we do for special occasions we enjoy the above for a most tender cut of beef.
Here is the way our family does it. There are other methods of seasoning and roasting but we are always satisfied with the results this way.
Try to buy a whole fillet that is already "peeled " ( trimmed of silverskin, fat etc. ) or if you prefer you can buy untrimmed and do it yourself.
The whole filet has a taped part ( called the tail ) and when you roast, tuck this part under so you can have a more even piece of meat for roasting.
If the whole filet is too large to fit your roasting pan you may cut the filet in half and roast the two parts in the pan together.
Make sure the meat comes to room temperature prior to roasting for even roasting which also helps with tenderness.
Rub oil ( we prefer olive ) over the filet and then rub in seasonings such as salt , pepper, paprika, crushed garlic etc. The Montreal Steak Seasoning is a nice choice ( available in the seasoning or meat sections of supermarkets ) .
Or other people prefer to coat the filet with Dijon mustard and then roll the filet in finely crushed black or colored peppercorns prior to roasting.
Both ways are delicious.
Place the filet on a roasting rack over the roasting pan.
You can also place the filet over some beef bones in the pan which also act as a rack.
Preheat the oven to 475 degrees F.
Place the prepared filet on the rack and roast 20 minutes ( for a average 5 lb roast- ). Then decrease the temperature to 350F and roast an additional 20 minutes.
Remove the filet from the oven and let sit about 15 minutes before slicing.
This total time factor should produce medium rare. A heavier roast will probably need more roasting time and a smaller roast less time. The sitting times allows for best slicing and lets some of the juices settle etc. If you prefer you can check and rely on a meat thermometer to test so you don't under or over roast the meat..
Insert thermometer in the thickest part of the roast. Generally 120 to 130 F is rare and 130 to 140 F is medium rare. Remember the meat will continue to cook with "standing time" out of the oven.
Meanwhile make the mushroom sauce ( this is a natural and not thickened sauce ). In a large skillet over medium high heat cook the onion in some olive oil or butter until softened.
Add the sliced mushrooms and garlic and continue to cook and stir until the mushrooms have reduced in volume by 1/2 and become tender.
Add the vermouth, dashes of Worcestershire sauce and Gravy Master ( a browning/ caramelized color for sauces etc. ). Cook and stir another 5 to 10 minutes and then season to taste. If you wish you may add a few tablespoons of the pan drippings or a bit of beef bullion paste ( available in jars ) for a richer flavor.
The whole recipe really can serve quite a lot depending on how thick or thin you slice the meat. Leftovers reheat well.