Preheat the oven to 180? fan.
Put the yoghurt into a mixing bowl, add the sugar and whisk well. Add the eggs, one by on, mixing well in between, the the oil and finish the batter with the flour and baking powder. Mix to a silky-smooth batter.
Depending on which recipe you are following, add the flavouring ingredients now.
Grease the tin and dust with flour, then pour in the batter. With a greased knife, trace a line in the middle of the batter on top of the cake. This will help the cake to rise correctly in the middle. Bake for 30-35 minutes until a skewer inserted into the middle of the cake comes out clean.
Remove the cake from the tin and immediately wrap it with cling film to keep the steam and moisture inside the cake.
If you are making the chocolate icing, melt the chocolate with the salted butter and simply pour on top of the cooled cake. Sprinkle with sea salt to finish.