I chose to make the Potato/Portobello Gratin this week. I have to admit, I didn't love it. The mushroom flavor was a bit overpowering. All well. I think I will try it again without the mushrooms and maybe add some onions.
As a side note, if you have a KitchenAid mixer but don't have a shredder/slicer attachment put it on your Christmas list. It took about 4 minutes to shred the cheese and the potatoes. It was awesome!