In a large skillet, melt the butter and then add in the steak and brown it. This should cook for about 5-10 minutes until slightly browned, then add in 1/2 of the can of beef broth, onions, and garlic and continue cooking. Let this simmer for 10 minutes. (If you use mushrooms add these in as well)
Once this simmers, add in the remaining beef broth and flour then stir continuously until thickened. Next, mix in the sour cream and parsley then let this simmer for another 10 minutes until it reaches the desired consistency.