The perfect crumbly-topped pudding can be made by stirring a spoonful of cornflour and perhaps some sugar into some fruit, and then topping it with 3oz butter rubbed into 6oz flour, 2 teaspoons of ginger, 4oz ground almonds and 4oz demerara sugar, and then cooking it at 180C for about half an hour or so.
photo Goddards Pies Ltd ...though actually the crumble here doesn't look all that, well, crumbly, does it. Ah well.
If you're no cook, then in Britain a crumbly is an affectionate insult. It describes an old person.
They're generally not too fast-moving, so they're easy enough to spot.
Spot the Frippet: something crumbly. This word used to be crimble, and is probably from some German language. Before that it was perhaps something to do with the Latin grūmus, a heap of earth.