Step 1

Preheat oven to 425°F. Grease a 12-inch cast-iron pan with butter. Cut each potato crosswise into 1/8-inch-thick slices without cutting all the way through to bottom and leaving about 1/4 inch of potato intact (this will help them hold together). Arrange potatoes in pan 1 inch apart. Brush with 2 1/2 tablespoons butter. Sprinkle with 1 teaspoon spices.

Step 2

Cover pan with aluminum foil and bake 30 minutes. Remove foil and drizzle potatoes (which should have opened up slightly) with remaining 2 1/2 tablespoons butter and 1 teaspoon spice rub. Bake, uncovered, until potatoes are crispy on edges and soft in the middle, 15 to 20 minutes. Garnish with parsley. Serve with sour cream alongside.