One 1 ½ to 2-quart gratin dish or other baking dish, buttered
Instructions
Set a rack in the middle level of the oven and preheat to 425 degrees.
Peel and slice the potatoes thinly – it doesn’t matter if they break up.
Arrange half the potato slices in the prepared dish and season with salt and pepper. Scatter the scallions on the potatoes, then cover with the remaining potatoes and season again.
For the custard, whisk all ingredients except the cheese together and pour over the potatoes.
Bake the gratin for about 15 to 20 minutes, or until just set. Sprinkle with the cheese and continue baking for about 10 minutes longer, to melt and color the cheese.
Allow the gratin to cool for 5 minutes, then serve immediately.