Pre-heat the oven to 180C and grease an oven-proof dish
Chop the fruit into bite-sized chunks (peeling the apple is optional) and place in a saucepan with the blueberries (if using), butter and cornflour.
Heat gently and stir until the butter has melted and the stone fruit has softened a little but still keeps its shape. Transfer the fruit mix to the greased oven-proof dish
For the topping, combine all the ingredients and mix well. Spread evenly over the top of the fruit in the dish.
Bake covered with foil for about 25 minutes, then remove the foil and continue to bake for another 10 minutes or so until the topping is golden and the filling is beginning to bubble up around the edges.
Serve hot with whipped cream or creme fraiche.