Tip the potatoes into an ovenproof dish, ideally lined with baking parchment, and scatter the brown sugar and small knobs of butter over the top.
Place the dish in a preheated oven at 180°C fan (200°C conventional oven, top and bottom heat) and cook for 45-55 minutes.Turn the potatoes every 10-15 minutes.
Let the potatoes stand for a few minutes before serving, turn them well in the caramel and tip them into a bowl.As the potatoes stand, the caramel will thicken slightly, and what has collected in the bottom of the dish will set around the potatoes.