Put the peach wedges and blueberries into a mixing bowl. Sprinkle over the caster sugar, cornflour and cinnamon and toss together to coat all of the fruit.
Preheat the oven to 190°C (170°C fan oven) Gas Mark 5. Spoon the fruit into a deep 23cm pie dish.
Unroll the pastry then brush all over with some beaten egg and sprinkle over the granulated and Demerara sugar. Use a pizza wheel cutter to roughly slice the pastry into lots of squares. Haphazardly put them all over the top of the fruit and pie dish rim – it doesn’t matter if you leave patches of the fruit showing through.
Bake for 35-40 minutes until the pastry is dark golden and crisp. Best served with vanilla ice cream, frozen yogurt or crème fraiche.