Parmesan-Crusted Potato Gratin With Pine Nuts

Preheat oven to 400°F with oven rack in middle of oven. Cook butter, oil, and thyme in a small skillet over medium until butter is melted and bubbling, about 1 minute. Remove from heat; set aside.

Peel potatoes; thinly slice each, keeping slices in order and forming 6 to 8 stacks of slices that taper toward the top. Arrange stacks of potato slices in a 10-inch cast-iron skillet, fanning out stacks as you place them in skillet.

Brush potatoes with half of butter mixture. Roast at 400°F until lightly browned, 40 to 45 minutes. Brush with remaining butter mixture; roast until crispy edges form on potatoes, about 15 minutes. Turn broiler to high. Sprinkle potatoes with cheese and pine nuts; broil until cheese is melted, 2 to 3 minutes. Sprinkle with salt.