This quantity will fill one baking tray measuring 30x50 cm and makes about 40-60 portions.
Use soft butter at room temperature for the cake batter.
Do not add the eggs all at once or the batter will split.
Use pastry flour rather than bread flour to avoid a chewy cake.
Use preferably tart apples like granny smith or Braeburns. Adjust the amount of sugar to taste. The custard powder will bind any liquid that comes off the apples. Possible add-ins are raisins, chopped nuts, dried fruits and ground cardamom.
Do not overcook the cake since it will continue cooking for a spell when cooling