1 1/2 pounds beef sirloin steak, 1/2 inch thick.
8 ounces fresh mushrooms, sliced (2 1/2 cups)
2 medium onions, thinly sliced. (Can reduce to one medium if necessary, but it changes both taste and final servings)
1 garlic clove, finely chopped. (Can go with two or three if you're bonkers for garlic, but no more than that)
1/4 cup butter or margarine. (I strongly recommend actual butter for both flavor and health reasons compared to margarine)
1 1/2 cups beef broth.
1/2 teaspoon salt.
1 teaspoon Worcestershire sauce. (Or to taste, but it really doesn't take much)
1/4 cup all-purpose flour.
1 1/2 cups sour cream.
3 cups hot cooked egg noodles.

Cut beef across grain into about 1 1/2x1/2-inch strips.

Cook mushrooms, onions and garlic in butter in 10-inch skillet over medium heat, stirring occasionally, until onions are tender; remove from skillet. Unlike a lot of dishes, caramelizing the onions is not good thing, follow this step exactly.

Cook beef in same skillet until brown. Stir in 1 cup of the broth, the salt and Worcestershire sauce. Heat to boiling; reduce heat. Cover and simmer 15 minutes.

Stir remaining 1/2 cup broth into flour; stir into beef mixture. Add onion mixture; heat to boiling, stirring constantly. Boil and stir 1 minute. Stir in sour cream; heat until hot (do not boil). Serve over noodles.

Now, this is essentially the Betty Crocker recipe. Not much has been changed since most people love that recipe and it was what a lot of families used whether they knew it or not.

However, there is room for change there. There's no specific mushroom given, as an example. Typically, it would be button mushrooms. I favor Portobello. But any mushroom that isn't so delicate as to be ruined, or so intense as to compete with the beef is fine. If you go with a Portobello, remove the gills before cutting it up, they make the final dish look like crap, and run a little bitter (imo).

You can make your own noodles as well, but that's a ton of work for little return.

You can use other cuts of beef. Sirloin is very good, but pricey. Stew beef works well as long as you extend the cook time a little before the final step. Same with cube steak. The texture and flavor changes, but not too much in the flavor. In both cases, you'll end up needing more stock to balance out the extra loss of water. Skirt steak works too, but I find it doesn't have a good texture in this application.

And, in a pinch, you can use water instead of stock, but it will not be as good. If you can't do beef stock, any decent stock will work better than water, even vegetable stock which has a totally different flavor in the sauce.