Heat the oven to 180C/160C fan/gas 4, with a shelf in the centre of the oven. Oil 2 x 20cm loose-bottomed cake tins and line the bases with baking parchment. Add the yogurt, milk, vinegar, eggs, soy sauce, olive oil and ¼ tsp fine salt to the bloomed cocoa powder, then whisk well until there are no lumps.
