Preheat the oven to fan 160C/ conventional 180C/gas 4. Boil the whole potatoes in a large pan for about 15-20 minutes until they are cooked – the timing will depend on their size. Drain and leave to cool, then peel off the skins and cut the potatoes into 5mm thick slices.
Put the butter and garlic in the pan the potatoes were boiled in, season and melt over a low heat. Add the potato slices and toss until just coated –but don’t let them fry. (You can prepare up to this stage the day before and keep covered in a cool place.)
Spread the potatoes out in a deep 28 x 22cm ovenproof dish and pour on the milk and cream. Sprinkle the cheese on top and bake for 30 minutes until golden and the potatoes are just beginning to crisp.