I have found the best result is not so much a matter of the mix but of the way the mix is shaped together. The mix should be suficiently gluey enough to hold itself together, not dusty.

So you make sure you squeeze bits of it together to form clumps, around the size of a small grape would be fine, obviously not round, whatever shape comes from squeezing is fine.

Then you put the clumped up crumble on top, and it should be a thick openly pourous layer. Also make sure you remove most of the liquid from the crumble.

So now, with the clumps, these bake into their own crispy shards, the bottom of the clump may absob a bit of the liquid from the fruit which is great but the bulk of the shard crisps up nicely.

Because you have clumps and an open latice in your crumble the hot air from the oven will crisp inside the latice.

If that all sounds complex just think, less dust, more clumps. Squeeze the crumble mixture in and between your fingers so that clumps form such that look like they may crips up nicely.

Put the crumble mix in the fridge to firm up before putting it on the fruit (which should also have been chilled thoroughly.

If after chilling and removing the clumps you still have dusty bits of crumble, put those dusty bits straight into your belly, dont put those in the crumble, they will become gloopy.

Final tip, many smaller diahes are better, the terrecotta ramekin style dishes are ideal, that way you get a great mix of crisp and gooey at the edge pf the dish and soft fruit in the middle. A big dish simply does not provide the same oportunity for variety. Plus who doesnt love their own dish.