Apple Gratin

2 1/2 lbs. Yukon Gold potatoes, peeled and cut into 1/4-inch-thick rounds 2 lbs. Braeburn or Pink Lady apples, peeled, halved, cored, and cut into 1/4-inch-thick slices * Lightly oil a 13 x 9 x 2-inch glass or ceramic baking dish. * Melt 6 Tbsp. ...