Pre-heat the oven to 175°C (350°F) and grease/line two 8 inch cake tins.
Melt the dark chocolate and then add the hot brewed coffee. Stir to combine, and set to one side.
In a large bowl, or using a food processor (which I did), beat the butter and sugars together until light and fluffy. Add the eggs one at a time.
Pour the chocolate/coffee mixture into the butter/sugar and give it a quick burst just until everything is evenly distributed.
In a separate bowl, combine the cocoa, flour, baking soda and vanilla sugar.
Mix the cream and milk together in another bowl. While the processor is running, slowly add one third of the dry ingredients to the butter/chocolate mixture, and then one third of the milk/cream. Repeat until you've added everything (don't over mix - just continue until everything is combined).
Divide the batter fairly evenly between the two pans and bake for around 20-25 minutes. The cakes are ready when the tops are fairly springy and an inserted skewer comes out clean. Remove from the oven and let the cakes sit in the pans for ten minutes or so, before turning out onto a wire rack to cool completely.
While the cakes are baking, prepare the coffee syrup: Heat the coffee, sugar and water in a pan, just until the sugar has dissolved and there is a rolling boil. Remove from the heat and allow to cool.
For the frosting: Beat the mascarpone together with 100g (1 cup) of icing sugar. Gradually add more icing sugar until you have achieved a thick, spreadable consistency, and it suits your personal sweetness level.
To assemble: With both cakes top side down, gently make little holes (I used a knife) all over the surface. Pour the coffee syrup evenly over both cakes. Let the cakes sit for a short while to allow the coffee to soak right in.
Slather over just under half of the frosting on one cake and then place the other one on top. Push down gently so that a little frosting squeezes out and then if you want to give it the same "naked" look as I have, take a little more frosting and smooth it along the seam where the cakes meet. Spread the remaining frosting on the top cake. When ready to serve, give it a very generous sprinkling of cocoa that covers the whole surface. Cut into gorgeous slices and enjoy!