It varies depending on what I have and/or how much butter I want to use, and I always make more sauce but (proportions to come later - this is off hand citation):

Make a roux, and add hot beef stock/broth, bring to boil and simmer for 2 mins, keep warm.

Melt butter in a pan until goes brown. Quickly brown the seasoned beef strips (1 lb total for 4 persons) in a minute (they say do a lb in two batches but more may be necessary), set aside with juices.
I often take the fat and other trimmings and render them in the pan, save the fat for yorkshire pudding, use the rest to cook.

Add more butter (or olive oil) to pan, let it melt until bubbling stops.

Sauté shallots (chopped) for 3-4 minutes until golden (need a lot more oil than suggested for that then add mushrooms (quartered, or sliced thick or thin, depending on mood) and sauté until juices release (YMMV on this one). Add back beef and juices, mix well, put in serving bowl or platter.

Add and stir in 3 Tbsp sour cream and 1 tsp dijon mustard to sauce while heating but do not let boil. Add black pepper (1/4 tsp) and salt to taste, and chopped dill (never have any around so usually substitute fennel fronds or chives). Pour over meat and serve on egg noodles (fortunately we can get German stuff here).

Just had leftovers from 2 nts ago (made a 4 person portion on 2 consecutive evenings - had Tournedos Rossini last night and will again tonight and probably tomorrow night too).

These latest batches used frozen beef broth that my wife used to boil daikon radishes for a pseudo scalloped potatoes dish. It's a bit sweet and watery so I added some concentrated (and salty) beef bouillon.