Preheat the oven to 180°C (350°F).
Melt the duck fat (or clarified butter) in an ovenproof dish or cast iron pan over medium heat. Add the garlic and cook for 1–2 minutes until soft and fragrant, without letting it colour.
Layer the potato slices in the dish. Sprinkle salt, pepper and half the parsley between each layer. Pour over any stock.
Cover the dish with a lid or aluminium foil and place in the oven. Cook for 35 minutes.
Remove the lid and cook for a further 15 minutes, until the potatoes are golden and crispy on top.
Rest for 5 minutes. Sprinkle over the remaining parsley and serve.