Preheat your oven to 170°C/150C Fan/gas mark 3/325ºF. Grease a 22 or 23 cm/ 9inch loose bottom tin with a little oil and line the base with baking parchment.
Measure and sift the cocoa powder into a bowl or jug and whisk in the boiling water until you have a smooth, chocolatey, still runny paste. Whisk in the vanilla extract, then set aside to cool a little.
In another smallish bowl, combine the ground almonds with the bicarbonate of soda and pinch of salt.
Put the sugar, olive oil and eggs into the bowl of a freestanding mixer with the paddle attachment and beat together vigorously for about 3 minutes until you have a pale-primrose, aerated and thickened cream.
Turn the speed down a little and pour in the cocoa mixture, beating as you go, and when all is scraped in you can slowly tip in the ground almond mixture.
Scrape down, and stir a little with a spatula, then pour this dark, liquid batter into the prepared tin.
Bake for 40-45 minutes or until the sides are set and the very centre, on top, still looks slightly damp. A cake tester should come up mainly clean but with a few sticky chocolate crumbs clinging to it.
Let it cool for 10 minutes on a wire rack, still in its tin, and then ease the sides of the cake with a small metal spatula and spring it out of the tin. Leave to cool completely.
Next make the dark chocolate cremeux put the chocolate in a bowl, mix the milk, cream and vanilla extract in a saucepan and bring it to the boil.
Whisk the egg yolks and sugar together until light in colour.
Add half the boiling liquid to the egg mixture, whisk until smooth and then add the egg mixture to the pan. Over a low heat stir the mixture until it reaches 84C and coats the back of a spoon.
Take the pan off the heat and strain through a fine sieve into the bowl of chocolate. Mix until smooth and then gradually add the butter until melted and smooth. Leave to semi-set for at least 30 mins at room temperature.
Next make the creme au beurre, put the caster sugar and water in a saucepan and bring to the boil and heat to 121C.
Put the egg yolks in the bowl of a stand mixer and whisk, slowly pour the hot syrup into the eggs and whisk until it is thick and cool.
Gradually add the softened butter while still whisking, When all of the butter has been added, add the orange juice and beat until light and fluffy.
When the chocolate olive oil cake has cooled, put the creme au beurre in a piping bag with a french tip fitted, place the chocolate cremeux in a piping bag with a straight nozzle fitted. Decorate the top of the cake with any pattern of your choice. I also added some candied peel to decorate the outer edges of the cake.