Add the baking soda to the yoghurt, stir well and leave it to bubble. In a separate bowl, beat the eggs with a mixer. To them, add the sugar and stir well again.
Next, add the baking soda with yoghurt and stir again. Next comes the flour, sifted ahead of time with the baking powder. Stir well and add the butter.
Pour the mixture into a buttered and floured baking form and bake in a preheated 356°F (180 °C) oven until ready.
After you take the cake out of the oven, release it from the form and leave it to cool completely. Then, using a knife (or thread) cut the cake into 2 parts horizontally.
Scoop out the insides of the lower half with a spoon and fill it with chocolate spread. Put the 2nd half back on top. Decorate with dark chocolate and coconut flakes.