Preheat the oven to 180 degree celsius. Lightly oil a silicone 23cm / 9inch cake tin and push a piece of baking paper into the tin so the baking paper is coming out over the edges as they will act as handles when we need to remove the cake from the tin. The cake will have a crinkle look from the baking paper but this is what we are looking for.
Break the chocolate apart and place into a heatproof bowl over a pot of boiling hot water and whisk until melted. Make sure the bottom of the bowl is not touching the water. Once fully melted, take off the heat and leave to slightly cool.
Separate the egg yolks from the egg whites. In a large mixing bowl, whisk the egg yolks, half of the sugar, melted chocolate, olive oil and clementine juice and zest until all ingredients are well combined.
In a stand mixer on the highest speed, mix the egg whites with a pinch of salt until they become stiff. Once the egg whites are stiff, gradually add the remainder of the sugar 1 tablespoon at a time in 1 minute intervals. Whisk until the egg whites are stiff, smooth and glossy. Gently fold the egg white mixture into the cake batter, being sure to be as gentle as possible to not break any air pockets. It’s okay if the batter is marbled and the egg whites are not fully mixed through.
Pour the batter into the cake tin and bake for 50 minutes. Leave the cake to rest in the cake tin for 15 minutes before removing it from the tin. Place onto a cooling rack and lightly dust with icing sugar and extra clementine zest.