Since you never know when you might be in urgent need of a crumble, I make up enough topping for at least 4 of these and let it sit safely in the freezer until required. Sprinkle it over your fruit of choice as it is, and cook from frozen. Sounds easy, doesn't it?
As for the fruit, I take all chopping out of the equation and give it parity with the crumble topping by using frozen mixed summer fruits; "jumbleberry" is just an old, English term for whatever mixture of berries were used in jams or puddings or jellies.
Recipe posted by Nigella