Preheat the oven to 325°F / 170°C. Grease a 9in / 23cm springform pan.
Whisk 50g of unsweetened cocoa powder with 125ml of boiling water to a smooth, runny paste. Whisk in 2 teaspoons of vanilla extract.
Mix 125g of all-purpose flour, ½ teaspoon of baking soda, and 1 pinch of salt.
Beat 200g of superfine sugar, 150ml of regular olive oil, and 3 large eggs for about 3 minutes, until thick and pale. Mix in the cocoa paste, then the flour mixture.
Pour into the pan and bake for 40-45 minutes, until the sides are set but the very center still looks slightly damp.
Cool in the pan on a wire rack for 10 minutes, then run a thin knife around the edge and unmold.
