There are few sights as uplifting in the kitchen as a golden, bubbling gratin coming out of the oven. It’s strange to be saying this, but one of the reasons I love this particular gratin is that it isn’t too creamy and rich. And the relative thinness of the wine and milk the potatoes and mushrooms are cooked in — relative to heavy cream, that is — is what allows you to cook this in such a hot oven and so quickly.

The first two times I cooked this, I peeled the potatoes; now I don’t bother. It isn’t necessary (and I buy baking potatoes that come all clean and shiny) and even if peeling them doesn’t really take long, it’s a good psychological step to remove: this is now a quick slice and chop, in a pan and thence to the oven. It feels easy — but then it may be because it is easy.