A gratin is a dish that has a crispy, golden topping. The topping can be achieved by covering the food item in question (often potatoes, cauliflower, or seafood, though it could also be fruit; see below) with buttered bread crumbs and/or cheese and heating it in the oven or under the broiler until brown and crunchy. (Although many people assume that gratins must have cheese, this is simply not so. It's the crunchy topping that distinguishes a gratin, not the cheese.) Dishes prepared in this way may also be referred to by the terms au gratin or gratine.
The ideal dish for creating a spectular gratin is round or oval, ovenproof (usually ceramic), and shallow; such a vessel increases the surface area of the food exposed to the broiler, thus insuring that each diner has a larger crispy portion of said dish.
Fresh Berry Gratin
This is delicious and extremely easy to prepare: a dynamite combination, in my books!
Preheat the oven to 400°F (200°C).
Break the croissants or muffin up into chunks and place in a food processor or blender. (If you don't have such kitchen appliances - poor you! - you can break use a knife to chop the croissants, or use your hands to crumble the muffin.) Add the butter and sugar if using and pulse a few times till coarsely chopped and mixed.
Spread the berries in a gratin dish; ideally they should be one or two layers thick. Sprinkle the topping evenly over the top.
Bake till the topping is browned and the berries are soft, 15-20 minutes. Serve warm with a spoonful of crème fraîche or sour cream. Yum.