1 Heat the oven to 180°C (160° fan) 350°F gas 4. Butter a 2 litre gratin dish.
2 Heat the stock, cream and milk in a pan with the garlic and bay leaf and bring to a boil. Remove from the heat, cover and leave to stand.
3 Mix the potatoes, leeks and ham together in the dish, and spread out in an even layer. Pour over the stock mixture. Season with salt and pepper and sprinkle with the cheese.
4 Loosely cover with foil and bake for 30 minutes. Remove the foil and bake for a further 30-4o minutes, spooning some of the stock mixture over occasionally, until the potatoes are tender. Allow to stand for 10 minutes before serving