Culinary definition of au gratin: To serve a dish au gratin is to brown the top under a broiler or in a hot oven, before serving in the original baking dish. Traditionally, au gratin dishes are topped with cheese, bread or cracker crumbs, or a combination of both.
C@H FOOD FOR THOUGHT
Use caution when browning bread or cracker crumbs as they burn easily and can dry out very quickly.Using broth and olive oil-moistened crumbs (the consistency of un-cooked poultry stuffing) is a good compromise as they develop a savory and crunchy skin under fire, but stay beautifully moist inside.
Cheddar and Gruyere cheese melt beautifully and evenly without too much fuss. Crumbly cheeses like Chevre and Feta are lovely but impart stronger, more distinctive flavours and require diligent babysitting, so as not to burn.