Mix 1/4 cup milk, sugar and custard powder together until smooth.
Boil rest of milk over medium heat.
Mix custard powder mixture into milk, stirring continuously. Boil over a low heat until thick and smooth.
Remove from heat and stir in the vanilla essence. Leave mixture to cool completely.
Beat egg whites until thick and fold into the custard mixture.
Leave in fridge.
Roll out the pastry and cut in half to give 2 squares.
Place on a lightly greased baking sheet and bake in a preheated oven at 200 °C for 15 minutes until puffed up and golden brown.
To assemble, place 1 puff pastry square on a large serving plate.
Cover with half the custard mixture.
Place other square on top. Cover with rest of custard mixture. Decorate with fresh fruit slices, if desired. Place in fridge until required. Slice and serve. Makes 1 large custard slice