Beat the eggs with the sugar to whitening, and while continuously whisking, add the salt, oil, yoghurt with baking soda dissolved in it and the vanilla. Add the cinnamon and baking powder sifted together with the flour. Mix in one direction carefully.
Pour one part into a pre-greased and floured cake form, and mix the rest with the cocoa dissolved in hot water. Pour it carefully over the white part and put the cake to bake in an oven preheated to 356°F (180 °C).
Do not open the oven for the first half hour, then check its readiness with a toothpick. Invert the baked cake onto a tray and optionally, sprinkle it with cocoa or powdered sugar.