You will need a baking dish approximately 22-24cm in diameter. Set the oven at 180C/gas mark 4. Quarter the apples, remove their stalks and cores, then slice each quarter into three.
Melt the butter in a shallow pan over a moderate heat, then add the apples and let them cook for 8-10 minutes until they start to soften, turning them over carefully with a palette knife.
Make the custard: break the eggs into a mixing bowl and beat with a whisk. Pour in the cream and milk, add the sugar, cinnamon and nutmeg and combine thoroughly then pour into a baking dish.
Crumble the ginger cake into large lumps and scatter over the custard. Add the apple slices then sprinkle with demerara sugar.
Bake for 35-40 minutes until the custard is lightly set – it should wobble a little as you shake the dish. Leave to settle for 15 minutes. Serve warm, though it is good thoroughly chilled too.