Preheat the oven to 200C/400F/Gas 6.
To make the apple crumble, put 50g/2oz of the butter into a small saucepan together with the ginger, apple and caster sugar and cook gently for 5 minutes until the apple has softened and broken down slightly. Pour into a small ovenproof dish.
Put the remaining butter, the flour and brown sugar into a food processor and blitz until it resembles fine breadcrumbs. Sprinkle the crumble mix onto the apple, place in the preheated oven and cook for 10 minutes.
To make the custard, put the milk, double cream and vanilla pod and seeds into a non-stick saucepan and heat until just boiling. Remove the vanilla pod and set aside.
Meanwhile, whisk together the egg yolks and caster sugar with an electric whisk until pale and fluffy. Pour the warm milk and cream mixture over the beaten eggs and sugar and whisk to combine. Pour the mixture into a clean saucepan and heat and whisk for a further 2 minutes or until the custard has thickened slightly. Remove from the heat and pour into a small jug.
To serve, pour the custard over the apple crumble.
