Had this at a friends house a few years ago. To say it was amazing is like saying that the most beautiful woman in the world is just a pretty girl!! Our first attempt to make it ourselves failed miserably because we thought we could just buy any old beef tenderloin. The only one that worked for us was the one we got at Costco. When I first read that we had to add water to the pan, I thought that someone was kidding when they added this to the recipe - but the finished product is absolutely wonderful. No need for steak knives with this roast.
poke the meat with a knife to make small slits all over. Set aside.
mix the bouillon cubes, garlic, mustard, tomato paste, pepper and worcestershire sauce. pour in ¼ cup of boiling water to dissolve the bouillon. using the back of a wooden spoon, crush the cubes. keep crushing and stirring until you have made a nice thick paste.
rub the paste all over the meat, rotating it to coat all sides well. transfer the meat to a roasting pan, cover loosely with foil and marinate for a minimum of 30 minutes or up to 1 hour in the refrigerator.
while the meat is marinating, set the oven rack to the middle position of the oven and preheat oven to 425.
pour enough water into the roasting pan to come to a depth of ¼ to ½ inch. place the pan in the oven and roast, covered with foil, for 15 minutes.
emove the foil and rotate the pan. continue cooking and check after 10 minutes that there is still liquid in the pan; add ¼ cup of hot water if needed. roast for an additional 5 minutes for rare, an additional 15 minutes for med rare and 20 minutes for medium or until the center of the roast registers the desired temp.
transfer the roast to a platter, cover with foil to keep warm and allow it to rest while you prepare the gravy.
place the roasting pan with all of the drippings on a burner over med heat. scrape up the brown bits with a wooden spoon add the butter and stir. whisk in the wine, sherry and broth. add the cornstarch water mixture whisking until thickened - another 2 - 3 minutes.