Preheat the oven to 180C/160C fan/gas mark 4
Beat the butter and caster sugar together in a stand mixer or by hand
Peel the apples, core them and chop them into chunks roughly 2½ cm
Place the apple chunks in an ovenproof dish to cover the base
Add the egg to the butter mixture and beat
Add the flour, salt and cinnamon to the mixture
Pour in the milk and stir together to form a batter
Spoon the batter over the apples
Warm the apple juice gently in a saucepan
Put the cornflour into a medium heatproof bowl
Pour the warm apple juice over the cornflour and stir continuously until thoroughly mixed
Scatter the dark brown sugar in a layer over the top of the batter
Evenly pour over the warmed apple juice mix
Place the dish on a baking tray
Bake for 35 minutes or until a skewer inserted into the cake part comes out clean
Take out of the oven and serve warm with generous amounts of custard or cream
