• Preheat the oven to 350f and grease and line two cake tins.
• Cream together the butter and sugar until light and fluffy then add in the egg and vanilla extract and beat until smooth.
• In a separate bowl sift together the flour, cocoa, baking soda and salt then add one spoonful at a time to the butter mixture and alternate with the sour cream and cooled coffee, starting and ending with the flour.
• Beat until just combined but do not over mix.
• Place into the oven to bake for around 25 minutes and until a toothpick comes out clean when inserted in the centre of the cakes.
  
• Once removed from the oven, allow to cool in the cake tin for ten minutes then remove to a wire rack to cool completely.
  

To make the chocolate hazelnut ganache:

• Place the sugar, cream and chocolate into a pan and heat on a low heat until melted and smooth.
  
• Remove from the heat then whisk in the nutella.
• Place into a bowl, cover and chill in the fridge until you have a consistency that will spread well but is not too runny. Stir occasionally whilst chilling as the outer edges set quicker than the centre of the ganache.

To assemble:

• Place a small amount of ganache onto a serving plate then place one layer of cake on top. Spread the top of the cake with the ganache then place the second layer on top.
  
• Spread ganache on top and around the edges of the cake and smooth with an offset spatula.
  
• Shave semi sweet chocolate across the top of the cake.