Slice your onions and mushrooms (with a little help, if desired).
On a covered skillet or large frying pan (with a cover), add the olive oil and butter, and brown the steak whole on both sides for a couple minutes each. (This seals in the juices and makes the beef cook tenderly.)
Remove from skillet, slice steak into strips and season with seasonings, and then toss the steak in a bowl with flour until completely coated.
While slicing the steak into strips, add the onion slices and mushrooms to the pan drippings and saute until onion is tender.
For the Cream Soup
In a small sauce pan by melting the butter. Once butter is melted, add the flour, and whisk until blended well and small beads form. Add broth and milk, whisk again, letting simmer until it thickens up. Add seasoning to taste.
Sprinkle the onion and mushrooms with a tablespoon of flour, then placed the floured steak back into the pan with the prepared cream soup and 1 cup of beef broth. Season again.
Stir then cover, cooking over low heat for about 30 minutes.
Every ten minutes or so, add more beef broth, mixing into the thickened gravy mixture, thinning it out a little, and add a dash more seasoning. Should use the remaining broth in the box by the end of the simmering time, to make it more gravy-like.
Once 15 minutes has passed since steak mixture began simmering, begin preparing egg noodles.
Once stroganoff is finished, stir in the sour cream right before you serve, and blend well. Serve over drained and cooked egg noodles.