Gratins are traditionally made with a number of vegetables, but the classic version in both France and the United States is the potato gratin, also known as gratin dauphinois or scalloped potatoes. Years ago, when I learned to make the dish, I took great pains to shingle layer upon layer of the sliced potatoes carefully into the baking dish before covering them with cream and cheese, repeatedly pressing down on the slices so that they'd remain submerged in the liquid while they baked. It was laborious and slow and, I later discovered, kind of a waste of time. No careful layering or ovenside tending is needed if you add a simple preliminary step: combine all the ingredients except the cheese in a pot, cook until the mixture thickens (the potatoes cook partially, releasing some of their starch and absorbing some of the cream), transfer the whole mixture to a casserole, top it with cheese, and bake. You still get the same, beautiful result but minus the fuss. Still, some traditionalists remain unconvinced. To them I offer a testimonial, e-mailed to me by my friend Charlotte Davis, a graphic artist in Boston. "The potato gratin was the star of the evening last night," she wrote after making it. "My husband, Tim, was appalled at the process and predicted failure or a nasty separation at the least. Hah! He ate his words."