2 2 1/2 lb pieces trimmed center cut beef tenderloin roast
1 TBS kosher salt
2 tsp fresh ground black pepper
3 TBS oil
3 TBS butter
1 1/2 lb fresh cremini mushrooms, cut into 1/2" wedges
1/2 cup medium dry sherry
Instant read thermometer
1 small carrot, chopped
1 medium onion, chopped
1/2 stick butter
1/4 cup all purpose flour
4 cups hot beef stock or reconstituted demi-glace concentrate
1/4 cup canned tomato puree
2 large garlic cloves, chopped
1/2 tsp whole black peppercorns
1 bay leaf
Put oven rack in middle position and preheat to 425ºF. Remove any strings from beef if tied, then pat beef dry and sprinkle with salt and pepper. Heat oil in a deep 12 inch heavy skillet over high heat until just smoking. then sear beef 1 piece at a time turning with tongs until well browned, about 5 minutes each. Transfer beef to an 18 by 12 inch flameproof roasting pan, reserving skillet.
Roast beef in oven to 120ºF, 20 to 25 minutes. Transfer beef to a cutting board, reserving roasting pan, and let rest, loosely covered with foil. for 25 minutes. Beef will continue to cook as it stands, reaching 130ºF for medium rare.
While beef roasts, heat butter in skillet add mushrooms, stirring frequently, until liquid they give off is evaporated and mushrooms are pale golden, 8 to 10 minutes. Remove skillet from heat.
While beef stands, straddle roasting pan across 2 burners, then add Sherry and deglaze pan by boiling over high heat, stirring and scraping up brown bits, Add sherry mixture and espagnole sauce to mushrooms and cook over moderate heat, stirring, until warm. Cover skillet and remove from heat.
Cut meat crosswise into 10 or 20 slices. Pour any juices on cutting board into sauce and heat over moderate heat stirring until hot.
Serve beef with 2 2/3 cups sauce.
Cook carrot and onion in butter until golden, 7 to 8 minutes. Add flour and cook roux over low heat, stirring constantly, until medium brown, 6 to 10 minutes. Add hot stock whisking constantly to prevent lumps, then add tomato puree, garlic, celery, peppercorns and bay leaf bring to a boil. stirring. Reduce heat and cook at a bare simmer uncovered, until reduced to about 3 cups, about 45 minutes. Pour sauce through a fine-mesh sieve into a bowl, discarding solids.