Method:

1. Melt the chocolate either in the microwave or in a large heatproof bowl suspended over a pan of simmering water (but not touching the water), making sure – either way – you remove it from the heat before it is completely melted, then stir it gently so that the last little pieces of chocolate dissolve. Leave to cool for 10 minutes. Stir in the oil and set aside.
2. Whisk the egg whites with a pinch of sea salt flakes in a grease-free bowl until you have firm peaks. Set aside.
3. Whisk the yolks, sugar and ¼ teaspoon of sea salt flakes in a separate large bowl until pale, thick and about doubled in volume.
4. Gradually pour the chocolate-oil mixture into the beaten yolks and fold to mix completely. Add a third of the beaten egg whites and fold in vigorously to lighten the mixture; no need to be delicate at this stage. Now gently fold in another third of the egg whites and, when that second lot is incorporated, fold in the final third leaving behind any liquid at the bottom of the bowl of whites. No white streaks should be visible.
5. Gently spoon the mousse into your ramekins or cups. To get the right texture – soft and satiny, rather than set like a more traditional mousse – you can either refrigerate for 20 minutes then eat straight away, or for an hour and then take out to come to room temperature for 40 minutes before eating.