Heat oven to 190C/fan 170C/gas 5.
Place the pears in a medium-size pan, add
the granulated sugar and cook on a medium
heat until the fruit starts to soften and
releases its juices, about 10 mins. Add the
blackberries and bring back to the boil, then
remove from the heat. Spoon the fruity
mixture into 4 individual ovenproof
ramekins, or 1 large baking dish.
Place the flour, butter and a pinch of salt
in a large bowl and rub together with your
fingers until the mixture resembles coarse
breadcrumbs. Add the pistachios and
demerara sugar, then stir to combine.
Sprinkle crumble evenly over the cooked
fruit. This can be done up to 1 day ahead,
or frozen for up to 1 month. Bake for 20-25
mins if small, 40 mins if large, until golden.
If baking from frozen, add 15 mins cooking
time. Remove from the oven, cool slightly,
then serve with ice cream, if you like.