Gratin Dauphinois

Heat the oven to 160C/325F.

Rub the cut face of the halved garlic clove over the inside of a 25cm baking dish and discard it.

Butter the dish generously with the softened butter.

Slice the peeled potatoes 2-3mm thick, on a mandoline if you have one.

Do not rinse the slices, however cloudy they look. The starch clinging to them is the only thickener in the dish, and rinsed potatoes bake in a thin liquid that never sets, so the gratin runs across the plate the moment it is cut.

Put the cream, milk, grated garlic, nutmeg, the 8g of fine salt, the ground white peppercorns and the bay leaves into a wide pan.

Add the potato slices and separate them with your fingers so none are stuck together.

Bring the pan to a bare simmer over medium-low heat, where bubbles break in two or three places only.

Never let it boil. Cream at a rolling boil splits into grains of protein and a slick of butterfat, and it does not come back together in the oven.

Cook for 8-10 minutes, lifting the slices gently off the base with a spatula every couple of minutes, until the liquid thickens enough to coat a slice and a slice bends without snapping.

Fish out the bay leaves.

Tip the whole panful into the buttered dish.

Press the slices flat with the back of a spoon, until the liquid rises just level with the top layer.

Bake for 55-65 minutes, until the top is deep gold and blistered and a knife goes into the centre with no resistance at all.

Lay a sheet of foil loosely over the dish if the top colours before the middle has softened.

Stand the gratin for 15 minutes before serving. Straight from the oven the sauce is still loose and floods the plate, and a quarter of an hour sets it enough to hold a cut edge.