Whip the cold cream for the mousse until it reaches a soft peak stage. Be careful not to whip it until it is stiff, or it will be hard to fold in and can split. Set it aside in the fridge.
Create a double boiler by placing a heatproof bowl on top of a saucepan of simmering water. Crack the egg into the bowl and whisk it until it is pale and frothy and warm to the touch. Make sure the bottom of the bowl never gets too warm; lift it occasionally to release steam.
Melt the chocolate in the microwave on low-medium and then stir in the extra virgin olive oil.
Stir the chocolate olive oil mixture into the whisked egg, then fold the whipped cream into it in thirds. Pour the chocolate olive oil mousse into glasses or ramekins and place them in the fridge for at least an hour.
Cardamom Chantilly cream
Whip the remaining cream until slightly thickened and gloopy, then sift in the sugar and add the vanilla bean paste and ground cardamom. Continue to whip until soft peak stage.
How to serve
Spoon some of the whipped cardamom cream onto the mousse, and drizzle over a little extra virgin olive oil. Sprinkle with a pinch of flaky sea salt and serve.
Notes
Storage The mousse can be made a day ahead, but take it out of the fridge 30 minutes before serving. Store leftovers covered for up to a day. The cream will keep in the fridge for 2-3 days.Use good-quality chocolate; Lindt, Callebaut, and Ghirardelli are good brands. Make sure your cream is high-fat and very cold.