Ultimate dauphinois potatoes

Method

1. Melt a knob of butter in a large, deep heavy-based frying pan or sauté pan over a medium heat. Add the onion and gently cook for 15 minutes until very soft and translucent. Remove with a slotted spoon and set aside.
2. Heat the oven to 180°C/160°C fan/gas 4. Add the garlic to the pan and gently cook for 1 minute. Stir in the milk, cream and nutmeg, then season well with salt and black pepper.
3. Meanwhile, peel the potatoes and slice as thinly as possible – about
   3mm thick (use a mandoline or an attachment on a food processor).
   Add the potatoes to the milk and cream mixture, stir gently, then bring to a simmer. Simmer for 20-30 minutes until the potatoes begin to soften. Tip into a deep tray and leave for 15 minutes until cool enough to handle.
4. Layer the potato slices and the onion in the prepared baking dish, packing them down as evenly and as neatly as you can. Pour the creamy liquid from the tray over the potatoes and pack them down with the back of a wooden spoon. Bake for 45-60 minutes until golden and cooked through. Cover with foil if browning too much. Sprinkle over the cheese (if using), then bake for 10-15 minutes until bubbling and golden. Mix the herbs and salt in a bowl, sprinkle on top and serve straightaway (or see Make Ahead; also see our tips below for how to prepare a cheffy make-ahead version). Serve with roast beef, duck or lamb.