The French expression au gratin is an everyday term in the culinary world, denoting a technique for preparing oven-baked dishes. In the 16th century or even earlier, the word gratin referred to the burnt, crispy bits of a dish that were stuck to the bottom of a pot or pan, which had to be grated or scraped off if they were not to go to waste.

Today, gratin commonly refers to any dish with a crispy baked topping. The ingredients for gratin most often include cream, grated cheese, and breadcrumbs, or a combination of the three. In addition to baking the dish uncovered in a hot oven, the au gratin effect can also be achieved by quickly browning of the top of a prepared dish under a broiler, giving it a nice crispy crust.

The technique is thought to have originated in Provence, but nowadays it is popular throughout the world. In addition to the famed potatoes à la Dauphinoise, gratin is a technique widely used in the preparation of various other vegetable-based dishes, as well as numerous meat, fish, and pasta casseroles.