Cod & Potato Gratin (Sugar Maple Day, 21st of Frost, Year 225)

Made Cod & Potato Gratin today -- used both my casserole dishes to do it. It's a pretty simple recipe, and I think it could be changed to be entirely pescatarian with a little work -- there's three strips of bacon in to that would have to be replaced, though I'm not sure what with -- mushroom bacon is the obvious choice, but I'm not sure it would work?

But it was quite good and I'd be willing to make it again if I see fresh or frozen cod on sale -- also Gruyere cheese, because it used up the last I had of that.