1. Bring a pan of salted water to the boil and add the potatoes. Reduce the heat and simmer for 10 minutes until just cooked. Drain and leave in the pan. Preheat the oven to 200°C/180°C fan/Gas 6.
2. Cut the lard and butter into cubes and dot over the potatoes. Sprinkle with sea salt and shake the pan so the potatoes are evenly coated and their edges scuff a little.
3. Tip on to a baking tray lined with baking parchment (you may need 2 trays). Roast for 35 minutes, turning, until crispy.