• Preheat the oven to  160°C Fan/180°C/350°F. 
• Lightly grease a 9 X 5" loaf tin, Line the bottom and sides with parchment paper, leaving an overhang on the sides for easy removal of the loaf after baking.
• In a bowl, sift flour, cocoa powder, baking powder, baking soda and salt. Set aside.
• In the bowl of stand mixer, beat butter and sugars until light and fluffy, about 5 minutes. Add eggs one at a time, beating well after each addition and occasionally scrapping down the sides of bowl. Add in vanilla extract.
• Mix in melted chocolate. With the mixer low, alternately add the flour mixture and buttermilk, beginning and ending with flour mixture.
• Dissolve espresso in hot water and stir into the cake batter until incorporated.
• Pour batter into the lined loaf tin. Put in the oven for 45-50 minutes or until a toothpick inserted into the cake comes out clean with a few crumbs sticking to it.
• Leave the cake to cool in the pan for 10 minutes and then using the parchment paper lift the cake out of the pan. Let it cool down completely on a wire rack .

Chocolate Mascarpone Cream

• Place the chopped chocolate and cream in a bowl safe bowl and microwave in 30 second bursts, stirring, until melted and smooth. Set aside and leave to cool before using.
• Beat mascarpone cream and icing sugar on low speed until smooth.
• Add the melted chocolate and whisk together until the frosting holds peaks. If the frosting is runny, cover with cling film and refrigerate for 1 hour before icing the cake.
• Spread the top of the cake with the frosting.