Preheat the oven at 160ºC fan / 180ºC.
Cream together the butter and light brown sugar in a bowl.
Add in the eggs and self-raising flour and beat together until all combined.
Pour 125ml of the coffee in the batter and add the walnuts.
Split the batter between four 8 inch baking tins.
Place in the oven and bake for 20 minutes.
Once baked, allow the cakes to cool on a wired cooling rack.
Meanwhile, beat the mascarpone with 75g icing sugar until light and fluffy.
Pour in the double cream and continue to beat until it forms a buttercream consistency.
Use the remaining cold coffee and sprinkle over the cake layers.
Layer the cakes with the mascarpone cream and place a thin coating around the outside to give it that semi-naked look. Allow to set in the fridge for 30 minutes.
Sprinkle over the cocoa powder and serve.