Preheat the oven to 350 degrees F. Thinly slice the potatoes, and then rinse in cold water and pat dry. Lightly butter a 9-inch cast iron frying pan. Arrange, in a fan-like way, a 1/3 of the potato slices in the bottom. Sprinkle with 1/2 the garlic slices and 1/2 the rosemary. Drizzle with a little melted butter, season with salt and pepper, and sprinkle on a 1/3 of the cheese. Repeat these steps again. Top with the remaining potatoes. Season with salt and pepper. Pour in the chicken stock. Sprinkle on remaining with parmesan cheese. Cover, being sure the foil does touch the cheese, and bake 50-60 minutes, or until potatoes are tender. Uncover, turn the oven to broil, and broil potatoes until the top is golden brown. If desired, garnish with small sprigs of fresh rosemary.
Note: It’s important to use freshly grated Parmesan cheese in this dish as the dried, pre-grated variety won’t melt the same.