Scrrrrrrrrumptious! Very, very good. I just used the steak that we had leftover from the previous dinner and it was just fine.
First I sautéed the onion in butter, then I put in the cooked steak until it was browned a little more. After all that, I just stuck to the recipe.
My husband really, really likes it (and he is a little picky), and would eat it again in a heartbeat... except he doesn't want to waste a fresh steak :D. We agree that this is the perfect recipe for leftover steaks.