Potato and Thyme Gratin

A gratin needs three things and cheese is not one of them. Potato, dairy and time. The starch that comes off the sliced potato is what thickens the cream, which is why the slices go into the dish unrinsed and slightly tacky.

Slice thin, and evenly

Two millimetres, and consistent. A mandoline is the honest answer. Uneven slices give you a dish that is simultaneously raw in one place and collapsed in another, and no amount of extra time fixes it.

Warm the cream and milk with the garlic and thyme first, then pour it over. Cold dairy on cold potato takes twenty minutes longer and the top sets before the middle has begun.

Press it down

Halfway through, press the whole thing flat with a fish slice so the top layer goes back under the cream. That is what gives you an even golden surface rather than a dozen curled, burnt edges.