I first came across a version of this voluptuously soft, rich chocolate mousse at Morito, one of my favourite places to eat in London. Then — as these things tend to happen — I started finding it everywhere. The olive oil doesn’t just bring its resonant flavour to the mousse, it creates its smooth, soft texture. Go for a smooth but still spicy rather than raspingly peppery extra-virgin olive oil, and use the absolute best quality you can. And please read the Additional Information section at the end of the recipe before proceeding. For US cup measures, use the toggle at the top of the ingredients list.