Butternut and red onion gratin

And I've skipped ahead to November 8th to make this accompaniment for the steak pie.  Regular readers will recall that I'm not a huge fan of mustard so this was just a little too mustardy for me - the others all liked it though so it's just my personal mustard discrimination at play.  I would make this again as it was very easy to make and quite showstoppy when served.