Be prepared to dirty up three sauce pans and a skillet when making this dish, but it's worth the extra cleanup. I suggest serving the meat and sauce over wide egg noodles, but if so you'd better start the noodles at the beginning.
1½ lbs. beef fillet, sirloin or porter house steak. Top sirloin will be less expensive, but less tender.
Salt and pepper
3 tbsp butter
1 tbsp flour
1 cup beef broth
1 tsp prepared mustard
1 onion, sliced
3 tbsp sour cream, at room temperature
Trim any fat and gristle from the meat. Cut into narrow strips about two inches long and one-half inch thick. Season the strips with salt and pepper and refrigerate two hours (I've never refrigerated the meat for more than 30 minutes myself).
In a saucepan, make a roux by melting 1½ tbsp of butter, add the flour and stir with a wire whisk until blended. Meanwhile, bring the consommé to a boil and add all at once to the roux, stirring vigorously with the whisk until the sauce is thickened and smooth. Stir in the mustard.
In a separate pan heat the remaining butter, add the meat and sliced onion and brown quickly on both sides. Remove the meat to a hot platter, discarding the onion. (Personally, I like to save the onion and add some of it back on the plate).
Add the sour cream to the mustard sauce and heat over a brisk flame for three minutes. Pour sauce over meat and serve. (An alternative is to add the sauce to the pan and cook for a few minutes to pick up the fond in the bottom of the pan, this colors the sauce a bit but adds greatly to the flavor).
About 6 servings.