Beef Stroganoff

When I was a child, the dinner I wanted for my birthday was often beef stroganoff. And oddly enough, it was often my husband's choice for his birthday dinner. My mother was given a recipe for beef stroganoff from one of the actual Stroganovs, and her recipe was an inexpensive version because after the fall of the Romanovs the Stoganovs also fell on hard times. There seems to be no true original recipe. This recipe is just another approximation.

1 1/2 pound beef sirloin, sliced into thin strips
salt and pepper
1/4 cup butter
1/2 large onion, diced or sliced or how ever you like the onions
2 cups beef broth
1/2 cup dry sherry (optional)
2-3 tablespoons tomato paste
1 tablespoon Dijon mustard
1 tablespoon Worchestire sauce
1/2 pound mushrooms
1 cup sour cream


to be continued

Sorry about the delay in getting back to this one.
The one important thing is to not add the sour cream until the very end, as it will curdle is cooked.