Sift the flour, "extinguish" the baking soda in the yogurt. Beat the egg with the sugar, add the yogurt and then the flour gradually, constantly whipping.
Finally add the oil, cinnamon, vanilla and rum. Pour the mixture into a greased and floured oven dish. Bake at 392°F (200 °C), and when it is nearly baked, check to see if it's ready with a toothpick.
The yoghurt cake is ready when after you poke it with a toothpick, no crumbs remain stuck to it.