Method
Preheat the oven to 180C/350F/Gas 4.
For that toffee apples, put the water and sugar right into a saucepan and gradually bring to the boil. Lessen the heat when the sugar has melted, add some syrup and butter after which bring to the boil again, stirring constantly.
Turn lower heat, add some apples and prepare, stirring lightly, until just soft. Put into an ovenproof dish.
For that crumble, rub the flour, butter and sugar together inside a bowl together with your fingertips before the mixture resembles breadcrumbs. Spoon the crumble evenly within the toffee apple mixture and put within the oven to bake for fifteen minutes, or until crisp and golden-brown.
For that custard, put the egg yolks and sugar right into a bowl. Put the milk and vanilla seeds right into a saucepan and produce towards the boil, then pour in to the egg and sugar mixture. Whisk until well-combined. Return the custard mixture towards the saucepan and warm on the low heat until it thickens enough to coat the rear of a spoon.
For everyone, divide the crumble between 4-6 serving plates and put a dollop of custard on every.