Double-layer custard and chocolate mousse  

Method

1. For the custard, put the cream, milk and vanilla extract in a large heavy-based pan over a medium heat and warm until just steaming. In a heatproof bowl, whisk the egg yolks with the cornflour and caster sugar until smooth and pale. Slowly whisk the hot cream into the egg mixture until smooth.
2. Return the custard mixture to the pan (no need to clean) and cook over a medium heat for 2-3 minutes until it forms a thick custard, whisking all the time. Divide the custard equally among 8 small bowls or glasses. Cover, then leave to set while you prepare the mousse.
3. For the mousse, melt the chocolate in a large heatproof bowl set over a pan of boiling water (don’t let the water touch the bowl) then set aside to cool slightly. In a separate clean bowl, whisk the egg whites and lemon juice until the whites form soft peaks when the whisk is removed. Slowly add the sugar, whisking between additions, until medium peaks form.
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5. Spoon a large spoonful of the egg whites into the melted chocolate, then stir in quickly until combined. Add the chocolate mixture to the remaining egg whites and fold in carefully using a large metal spoon until smooth and fully incorporated.
6. Spoon heaped spoonfuls of the mousse on top of the custard, dividing it equally among the bowls. Finish by grating over extra dark chocolate (or hazelnuts/Crunchie; see tip) then cover and leave in the fridge to set for 3-4 hours (seeMake Ahead).