- 285ml/10¼fl oz milk
- 285ml/10¼fl oz double cream
- 1 vanilla pod, split, seeds scraped out
- 6 free-range egg yolks
- 125g/4oz caster sugar
- 150g/5½oz plain flour
- 50g/2oz caster sugar
- 50g/2oz cocoa powder
- 100g/3½oz cold butter, cut into cubes
- 200g/7oz dark chocolate (minimum 70 per cent cocoa solids)
- 150ml/5½fl oz double cream
- 6 free-range egg whites
- 1 commercial foam gun (also known as an espuma gun; available in specialist cook shops and online)
- For the vanilla ice cream, place the milk, cream, vanilla pod and seeds into a heavy-based pan and bring to the boil. Remove from the heat, then discard the vanilla pod.
- Whisk the egg yolks and sugar together in a bowl until pale and fluffy, then slowly whisk in the milk and cream mixture until well combined. Return the custard to a clean pan and cook over a medium-low heat for 5-6 minutes, until it thickens enough to coat the back of a wooden spoon. Set aside to cool completely.
- Pour the custard mixture into an ice cream machine and churn according to the manufacturer's instructions. Spoon into a freezer-proof plastic container and chill in the freezer until ready to serve. Remove from the freezer five minutes before serving to soften.
- For the chocolate crumble, preheat the oven to 210C/410F/Gas 6.
- Sift the flour, sugar and cocoa powder into a bowl. Add the butter and rub together with your fingertips until the mixture resembles breadcrumbs. Spread the mixture out on a baking tray and bake in the oven for 10-12 minutes, or until golden-brown and crisp. Shake the tray halfway through the cooking time to prevent the crumbs from sticking together too much. Remove from the oven and set aside to cool.
- For the chocolate foam, place the chocolate and cream into a heatproof bowl set over a pan of just-simmering water (make sure the bottom of the bowl doesn't touch the water). Leave until melted, then whisk in the egg whites until well combined.
- Spoon the mixture into the foam gun and gently warm through in the pan of simmering water. Spray the chocolate foam into four serving bowls.
- To serve, top the chocolate foam with the crumble mixture and serve with a scoop of vanilla ice cream.