Preheat oven to 200°C
Prepare the fruit by pitting and halving the prunes
Mix prunes and blackberries with caster sugar, cornstarch, and vanilla extract
Pour fruit mixture into a baking dish
Make the crumble topping by combining flour, brown sugar, oats, and salt
Cut butter into small pieces and rub into the dry ingredients until breadcrumb texture forms
Spread crumble mixture evenly over the fruit
Bake for 30-35 minutes until golden brown
Allow to cool slightly before serving