Preheat the oven to 200°C.
Gently cook 50g butter, ginger, apple, and caster sugar in a saucepan for 5 minutes until softened.
Pour the apple mixture into a small ovenproof dish.
Blitz the remaining butter, flour, and brown sugar in a food processor until fine breadcrumbs form.
Sprinkle the crumble over the apples and bake in the oven for 10 minutes.
Heat milk, double cream, and vanilla in a saucepan until just boiling, then remove the pod.
Whisk egg yolks and caster sugar until pale and fluffy.
Pour the warm milk mixture over the eggs while whisking to combine.
Heat the mixture in a clean pan for 2 minutes until thickened, then pour into a jug.
Serve the warm custard over the apple crumble.