How to Make It
Preheat the oven to 400°F. Thinly slice the potatoes using a hand-held slicer. In a large bowl, toss the potatoes with the onion, milk, cream, 2 teaspoons salt and 3/4 teaspoon pepper. Transfer the potato mixture. Sprinkle the cheese evenly over the potatoes and cover with foil.
Bake the casserole until the filling is bubbling and the potatoes offer no resistance when pierced with the tip of a knife, 45 to 50 minutes. Uncover the casserole and preheat the broiler.
Broil the casserole about 3 inches from the heat, until golden in places, 6 to 8 minutes.