- 5 or 6 Yukon gold potatoes, peeled
- 2 or 3 Portobello mushroom caps, sliced thin
- 1 cup grated hard cheese such as Parmesan or Asiago
- 3/4 cup half and half or cream
- Kosher salt and ground black pepper
Now, a gratin is basically just a casserole constructed out of thin slices of potato layered with, well, whatever you salvaged from the refrigerator.
Now, medium starch potatoes like these Yukon Golds are really perfect gratin fodder because they'll bind together when they cook without losing their consistency.
Butter your casserole first because believe me this will set up like concrete if you don't. I've been there. So, it's a lot like building a sky scraper. We're just going to put down a layer of potatoes and then we're just going to put the other ingredients on top and then repeat it until we've got about 4 layers down.
Now, some mushrooms. You want to go kind of light on the mushrooms because they'll form a barrier in between the lower and upper potato layer and that will keep the gratin from setting. You'll end up with chowder instead of a gratin. A little bit of parsley, not much. Some salt, more than you'll think you need because potatoes always need salt. A few grinds of pepper and a little bit of that Asiago cheese. Again, that's going to go on every layer so go easy. You don't have to put a load on every single layer.
So, we're just finishing up the 4th layer of the gratin. Great. Now, before we put on any other ingredients we're going to add some dairy and that's going to enrich the flavor. It's also going to aid the consistency, help the whole thing to bind together.
Anyway, I add about half a cup and then we're going to squeeze the whole thing. Now that's to get the Half & Half really distributed and also to get all of the air bubbles out. Now, I know I've got enough in there because it's coming up around the edges, so that's great. Now, I've got a 400° oven. Anywhere between 400 or 450 is fine.
Now, for about the first 45 minutes of cooking I like to cover this with foil very loosely. I don't want to trap the steam in there but I do want it to stick around a little bit and help the potatoes cook. Doing this also helps us to not over brown the top which is, of course, just another word for burning.
So, we pulled the foil off about 10 minutes ago to let the top brown. It looks pretty good.
Now, the only way to really tell if this is done is to give it a few pokes with a sharp knife or fork. If the blade really goes in easily but you can just kind of feel a delineation between the layers, it's dinner time. Well, it's almost dinner time because this really will be a lot better if it's allowed just to sit for, say, 15 to 30 minutes. That way the layers will bind up really nice and you'll be able to cut it into wedges easily.