O-gratin is a French term that means a way of baking a dish with a delicious crispy crust. Typically used in pies and casseroles.
Grated cheese or sour cream will help give a salty dish a crispy crust – just add these ingredients 20 minutes before turning off the oven. But you can use them from the very beginning – it depends on the time and ability of the dish to bake.
Another option is to sprinkle breadcrumbs on the cake and top with grated butter. For a sweet cake, replace the crackers with semolina.
Cottage cheese casserole and muffins will acquire a golden crispy crust if you sprinkle the surface with sugar – this will also add a caramel flavor to the dish.