3poundsrusset potatoes, peeled and sliced 1/8-inch thick (see note)
Salt and pepper
¾cupheavy cream
½cuplow-sodium chicken broth
Instructions
Preheat the oven to 350 degrees and adjust an oven rack to the middle position.
In a large bowl or ziploc bag, toss the cheeses and cornstarch together until evenly coated.
IMPORTANT: See note below for size of pan to use.
Layer half of the potatoes in the bottom of the pan overlapping slightly in a shingle-type pattern.
Sprinkle the potatoes evenly with 1 1/2 cups of the cheese mixture, 1/2 teaspoon salt, and 1/4 teaspoon pepper.
Top with the remaining potatoes, shingling them neatly and evenly over the cheese. Sprinkle another 1/2 teaspoon salt and 1/4 teaspoon pepper evenly over the top.
Combine the cream and broth in a large measuring cup and pour the mixture over the potatoes.
Sprinkle the remaining cheese mixture over the top and bake until golden brown and a fork inserted into the center slides in easily with little resistance, 75 to 85 minutes (check the potatoes after 60 minutes if baking in a 9X13-inch pan).
Let the potatoes cool for 10 minutes to set up. Serve warm.
Notes
Pan Size:The original recipe called for making these potatoes in a 2- or 3-quart gratin dish, which can range anywhere from 7 to 10 inches in length (and is often oval shaped).
If you don't have a gratin dish, this recipe can be baked in a dish of an equivalent size (see following notes).
A 9X13-inch dish is considered a 3-quart dish. If using this dish for these au gratin potatoes, the assembled layers will be thinner than if baking in a smaller dish, so the baking time will likely be shorter (check after about 60 minutes). The recipe can be increased by half (so 1 1/2 all the ingredients) and baked in a 9X13-inch pan for thicker layers.
Other pan sizes, like a 9X9-inch pan or a 10 1/2-X7 1/2-inch pan can be used for a thicker potato casserole.
Slicing the Potatoes: It is hard to get the potatoes thinly and evenly sliced by hand, but not impossible. A food processor fitted with a slicing disk set to 1/8-inch, as well as a mandoline, works great to slice the potatoes evenly.