A crumble is a spiced flour, sugar and butter mixture that is “crumbled” over top a filling before baking. The filling is usually fruit.
There are also savoury crumbles.
If you are looking for the difference between a crumble and a cobbler, the topping for a crumble is kind of a “shortbread” one, with butter and sugar rubbed into flour and then scattered over the dish, whereas a cobbler is more of a “biscuit” topping (biscuit in the North American sense, being a flour, baking powder and water/milk mixture.)
The “flour” can be all wheat flour, white or whole-grain, or flour from another grain, or a mixture of flour and another grain such as rolled oats, or all rolled oats, etc.
By the start of the 2000s, crumble had become all the rage in France, in homes and in restaurants. Its Englishness appealed to the restaurant-going public; at home, they like the simplicity of making the dish. The French, though, have popularized both types of crumble, “les crumbles salées et sucrées” — savoury and sweet crumbles. You’ll see dessert crumbles with names such as Crumble de prunes à l’anis, Crumble aux pommes, Crumble aux kiwis, as well as savoury crumbles such as Crumble à la tomate et au cumin, Crumble de courgettes et tomates, Crumble de noix de coco au curry de dinde, and le Crumble salé au caviar d’aubergine et crème de parmesan.
Crumbles are very good “make ahead” desserts: you just reheat them in a moderate oven until they are bubbling hot.
You can use Muesli or granola to act as a crumble topping; just sprinkle it over top your dish.
To make a complete cheat’s crumble, put 2 tins of drained fruit in a baking dish, sweeten and spice to taste, sprinkle granola on top, and pop in oven to heat and brown.
Instead of butter, a small amount of low-fat or non-fat sour cream can be used to reduce calories in the topping.
Called Crumble in the UK; Crisp in North America.