(pen) Can't stand rhubarb. But blackberry and apple crumble, the very thought..... drools...... You're quite a gardener, then? Not I; just keep it tidy, keep the wilderness under control.
[INJ] Then make your pre-fool (rhubarb puree) now, freeze it until the raspberries are ripe, then add the cream to make the fool and add the fresh raspberries.
Sorry, ladies and gentlemen, crumbles are to me similar to shortbread. Should I have some medical condition which involved over salivating then each or either could be a solution. As I do not suffer from such a condition (yet) both species of those concoctions that seem to mimic the absorbent quality of some sort of surgical swab are well and truly off the menu.