Preheat the oven to 180°C.
Peel, core, and roughly chop the apples.
Place apples, lemon juice, and water into a saucepan.
Cover and cook briskly for five minutes until apples soften.
Stir in the 20g of butter and first portion of caster sugar.
Transfer the mixture to a 900ml capacity ceramic dish.
Let the apple mixture cool while preparing the topping.
Cream the 75g of butter and remaining caster sugar until light.
Gently fold in flour and eggs alternately until blended.
Add one tablespoon of boiling water to the batter.
Spoon batter over apples and bake for 30 to 35 minutes until golden.