Exactly as the title says, these are cooked in a muffin or Yorkshire pudding tin! They are a brilliant way to use up leftover potatoes & are so good that it's worth baking or boiling up some potatoes specially!! I use these all the time in our Chambres d'Hotes - it's easy to work out the portions and they freeze beautifully. There is also NO burnt mess in your gratin dishes! That's not to say I never make traditional Gratin Dauphinoise, because I do - but these are a great standby, use up leftover potatoes and look very elegant when served!