Cut the potatoes into thin slices (no need to peel them; they are especially pretty left unpeeled if red-skinned). Ideally, use a mandolin or the slicing attachment on a food processor to speed things up.
Pour the cream and milk into a large saucepan and bring to the boil. Peel the garlic and add one whole clove to the pan with a good grating of nutmeg and the bay leaf. Season generously, and when the mixture is bubbling add the potatoes. Reduce the heat and cook for six minutes, so the potatoes just begin to cook.
Meanwhile, halve the remaining garlic clove and rub the inside of a roasting tray with its cut sides. Grease liberally with butter and then gently pour or spoon in the potato and cream mixture, discarding the garlic. Cover the tray with foil and bake for 45 minutes.
Place the breadcrumbs in a bowl and pick in the thyme leaves. Grate in the cheese and toss everything with a little olive oil.
After 45 minutes, remove the tray of potatoes from the oven, scatter over the breadcrumb mixture and place back in the oven, uncovered, for a further 30 minutes, until golden and cooked through. Allow to cool for five minutes before serving.