Stir the yoghurt with the baking soda until it becomes effervescent.
Beat the egg with the sugar, add the cocoa, vanilla and beat the entire mixture into the yoghurt with the baking soda.
Next, beat in the flour and oil until homogeneous.
Pour it into a buttered and floured form. Bake about 45-55 min. in a preheated 320°F (160 °C) oven.