Preheat the oven to 200°C, fan 180°C, gas mark 6. Melt the butter in a frying pan, add the leeks and sauté for 5 minutes or until really soft, stir in the nutmeg.
Thinly slice the potatoes they need to be the thickness of a one pound coin. Use a little of the butter from the leeks to butter an ovenproof dish. Cut the garlic in half then rub it all over the inside of the dish.
Scatter half the leeks over the base of the dish, top with half the sweet and ordinary potatoes, overlapping the slices.
Repeat ending with a neat layer of potatoes on top.
Mix the cream and milk together with a little salt and plenty of ground black pepper and pour over the potatoes, cover with foil.
Bake for 40minutes remove the foil and scatter over the cheese. Bake for a further 25-30 minutes or until the top is golden and the potatoes are tender. Leave to stand for 5 minutes before serving.
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