I've picked some rhubarb at last, despite my earlier disparaging remarks, and as there's already quite a lot of it, I feel I should be using some, if only in the interests of seasonality. Crumble is always a winner in our household, and the sourest fruits seem to make the best crumble - Bramley apples, blackcurrants, and of course rhubarb.
This is my standard crumble mix:
1 lb/500g plain flour
6oz/150g demarara sugar
4oz/125g porridge oats
Whizz the flour and butter in the processor to breadcrumb stage. Add the sugar and oats and pulse minimally to just mix in. Tip into a plastic bag and keep in the freezer. To use, simply place your chosen fruit in a dish with enough sugar to sweeten, and top with the required amount of frozen crumble, according to who's eating it. In our house, if John's coming round, it's hold the fruit, heavy on the crumble for example.
Bake in a medium oven for about half an hour, depending on the size of your dish of course.
Best with cream, or custard, although some weird people like it with ice cream. There's no accounting for taste.