Beef Stroganoff

I have always liked Beef Stroganoff and have been trying to perfect it for awhile.  I think I may have finally found the right mix of ingredients.  One note regarding this recipe; make sure that you cut the meat into small pieces and pound it thin, if you don't the meat will be tough.

Beef Stroganoff:
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1 1/2 pounds sirloin tip (cut into bite size pieces and pounded very thin)
5 tablespoons butter
4 tablespoons vegetable oil
2 tablespoons flour
2 cups beef stock
1 onion, diced
8 ounces mushrooms, thinly sliced
6 tablespoons sour cream
2 teaspoons Dijon mustard
salt & pepper

Season the meat with salt and pepper.  Heat 2 tablespoons vegetable oil in a large skillet.  Brown meat (use additional 2 tablespoons vegetable for second batch if you need it.)
Remove meat to a plate, add 3 tablespoons butter to the skillet.
When butter is melted, add mushrooms and onions.  Saute for about 5 minutes.
Add 2 tablespoons flour and stir for one minute.
Add beef broth and meat back in.
Stir, partially cover and let simmer for 30 minutes.
While simmering, heat water for egg noodles.
Cook noodles according to package, drain and mix with remaining 2 tablespoons butter, salt and pepper.
Add sour cream, mustard and salt and pepper to taste, to the stroganoff.
Serve over noodles.