Preheat the oven to 190°C, gas mark 5. Grease four individual ovenproof dishes.
Set a large saucepan with the pears, apples, caster sugar and vanilla seeds over a medium heat. Cook for 10 minutes, stirring occasionally, until the fruit begins to soften. Remove from the heat, stir in the blueberries, then divide among the prepared dishes.
For the crumble, put the flour, demerara sugar and ground almonds in a large bowl. Stir to combine, then rub in the butter with your fingertips until it resembles coarse breadcrumbs. Stir in the flaked almonds.
Spoon the topping over the fruit and bake for 25-30 minutes, until the fruit is bubbling and the crumble golden. Leave to cool for a few minutes. Serve with scoops of vanilla ice cream, if you like.