Today we had left over pork roast. I made a simplified Sauce Robert (I used beef stock instead of demi-glace.) It didn't come out as thick as a Sauce Robert, nor did I expect it to, since it didn't have any starch to act as a thickener, but the taste was close enough to the classic version I made two weeks ago that it went very well with the pork.
Next time I roast a chicken, I'm going to try a classic hunter's sauce, or Sauce Chasseur (mushroom sauce), with the rest of the demi-glace concentrate.