Preheat the oven to 200ºC, fan 180ºC, gas 6. Unroll the pastry, keeping the greaseproof paper attached to the bottom, and place on a baking sheet. Cut the pastry into 4 equal rectangles.
Arrange the sliced apple on each rectangle and scatter over the raspberries if using.
Sprinkle the brown sugar and cinnamon over the fruit, then brush the edges of the pastry with the milk. Bake for 10-15 minutes until golden and cooked through. Dust with icing sugar and serve warm.