Heat the oven to 180C/160C fan/gas 4. Mix together the fruit and granulated sugar (you will need less sugar for canned fruit) so it’s evenly coated. Tip into a pie dish where it fits snugly.
Rub the butter into the flour to make a light breadcrumb texture. Do not overwork it or the crumble will become heavy. Add in the demerara sugar until combined and spread over the fruit until completely covered.
Bake for 35-50 mins until golden brown and bubbling, and the fruit is tender. Leave to cool for 5 mins before serving.