Preheat the oven to 180 C or 356 F. Melt the unsalted butter and dark chocolate in a large bowl.
Stir in the vanilla extract
Leave the chocolate mixture to cool whilst you mix the flour, cocoa powder, baking powder and sugar together in a separate bowl.
When the chocolate mixture is room temperate, gradually add the eggs until they are well stirred in.
Gradually add the dry ingredients into the wet ingredients, the mixture should resemble a thick-ish paste.
Pour the cake batter into two greased cake tins and bake for half an hour.
Poke a skewer or thin knife into the centre of one of the cakes to check if it is ready. If it comes out with mixture on put them back in for 7 mins. If it comes out clean then remove them from their tins and leave to cool.
While the cake is cooling make the icing: combine the water, icing sugar, butter and cocoa powder in a bowl and blend into a paste.
When the cakes have cooled spread half the icing on top of each cake. Place them on top of each other and add any decoration that you want.
Enjoy (goes very well with vanilla ice cream)