Preheat oven to 210°C (190°C for fan assisted ovens)/Gas Mark 7
Unroll the pastry and lay on a lightly greased baking sheet. Mark the pastry with a knife 2.5cm from the edge and score in a crisscross pattern within the markings. Brush with the milk and place in the oven and bake for 15-20 minutes. Leave to cool and lightly push the pastry down in the middle where it has puffed up. Carefully transfer to a wire rack and cool completely.
In the meantime put the raspberries into a saucepan with the sugar and cook for 2 minutes then put aside to cool. Whip the cream until soft peaks form, then lightly fold in the custard to create a rippled effect.
To assemble, spoon the cream custard over the pastry and add the raspberries and any juices. Serve immediately.