I took winkki's comments to heart and added just enough water to the potatoes to cover the bottom of the casserole. I'm at a loss as to how to get golden potatoes AND lemony juices from one gratin dish. Loved the flavor of the potatoes but they don't crisp up and brown until the dish is dry. The onions retained that wonderul olive oil/lemon flavor but it didn't transfer to the potatoes and there were no juices left to pour on the fish. The cod definitely benefits from the same seasoning and lemon juice.
A nice change of pace from the usual ways of fixing cod. It was a bit vague regarding what seasonings were to be used for the cod, so I tried to echo the flavor of the potatoes: I used rosemary, thyme, oregano, salt & pepper, and a wee bit of lemon juice along with the olive oil. It made for a delicate, almost elegant, piece of fish. As far as the rest of the recipe, I've made a lot of Greek Potatoes, though never with water to cover (or rather, to 'barely cover') but went ahead and followed the recipe as written (well, I spooned out about 1/3 of the water when I turned the potatoes after 45 min; there was still plenty left by the time cooking was done). It worked fine, although they did stay a bit 'brothy' and much softer than usual, and perhaps a bit diluted as far as the seasoning goes (although, in all fairness, I had to use dried oregano; would obviously have been much bolder flavor with fresh herbs) We crumbled some feta over the potatoes as they were served which made up much of the flavor difference, and had steamed spinach with balsamic vinegar on the side (wish I'd had some toasted pine nuts to toss in to complete that Mediterranean flavor!). I'm sure we'll be making it again. Thanks!