These rich, soft creamy potatoes, tasting of nutmeg and garlic, are heavenly served with thick slices of ham. It is important to use gruyère here; its delicate flavour and relatively low fat content (for a hard cheese) lend a more refined taste than, say, cheddar. And do use waxy rather than floury potatoes; traditionally these are cut as finely as possible, but I like them with a little more body.