by adding "flame" (flambe), basically all you are doing is quickly evaporating the alcohol from the brandy. normally, you could do this by reducing the sauce, but the sauce for steak diane doesn't traditionally call for reduction. you can probably find a good recipe on google or yahoo. i don't have a recipe off the top of my head, but the sauce usually consists of heavy cream, brandy, butter, shallots, and tarragon.