Photo: Tara Fisher
Preheat the oven to 180°C/fan 160°C/gas mark 4. Put the chocolate and olive oil in a bowl and set over a pan of simmering water. Stir until completely melted, then set aside. Grease a 22cm springform tin and line the base with non-stick baking paper.
In a large bowl, whisk together the egg yolks and sugar with a hand whisk until the mixture is pale, thick and voluminous. Gently stir in the melted chocolate mixture.
In a clean bowl and using clean whisks, beat the egg whites until they form stiff peaks. Gently fold the whites into the chocolate mixture. Set the tin on a baking tray and pour the chocolate mixture into it. Bake for 30 minutes, then leave the cake to cool completely in the tin. To serve, release the cake from the tin and transfer to a serving plate or board. Dust the top with cocoa and serve with berries and ice cream.