1. Set the oven to 180°C/gas 4. In a large saucepan, bring the milk and garlic to the boil.
2. Add the double cream; stir well and season to taste with the salt, pepper and nutmeg. Add the potatoes and simmer gently for about 20 minutes until the potatoes are soft and the liquid has thickened.
3. Add half of the cheese and gently stir it in. Pour all of this into a shallow gratin dish and sprinkle with the remaining cheese.
4. Bake the gratin in the oven for about 15 minutes until wonderfully brown and bubbling on top. Serve piping hot.