Melt the chocolate and butter with the coffee in a heavy-based pan.
Mix together the flour, bicarbonate of soda, light muscovado sugar, golden caster sugar and cocoa powder in a separate bowl. Break any lumps with your fingertips.
Beat the eggs and stir in the buttermilk.
Pour the chocolate and egg mixtures into the flour, stirring to a smooth consistency.
Pour into your prepared tin and bake in a preheated oven.
Chop the chocolate for the ganache.
Heat the cream and sugar until nearly boiling and pour over the chopped chocolate.
Cut the cake in half or thirds and lift the layer or layers off.
Put the bottom layer on your serving dish and spoon on a little ganache over. Repeat with the next layer if you've cut your cake into thirds.
Put the top layer on the cake and pour over the remaining ganache.
Use a palette knife to smooth it over the surface.
Decorate with chocolate curls.