Pre-heat the oven to 180°C/ Fan 160°C/Gas 4. Rub some butter around the inside of two 18cm round baking tins or insert baking liners.
Measure the flour and cocoa into a bowl and stir to combine. Break the eggs, separating the yolks into one bowl and whites into another.
Put the butter and sugar into a large bowl and beat together until light and fluffy. Add the yolks and beat again. Stir in the coffee. Sieve the prepared flour into the bowl and mix well.
Beat the whites until stiff. Fold the egg white into the mix with a metal spoon using a cutting and folding action, taking care not to overmix.
Divide the mixture between the prepared tins. Bake for 18-20 minutes. If a cocktail stick pressed into the centre of the cake comes out clean, it is cooked. Turn out the cakes onto a wire rack and leave to cool.
To make the chocolate filling, break the chocolate into small pieces. Put the cream and sugar into a saucepan over gentle heat and stir as it warms. Remove from the heat just as it starts to bubble. Add the chocolate and stir until it has melted. Allow to cool and thicken. Spread the cold filling on one cold cake layer and place the second layer on top.
For the coffee icing, measure the icing sugar and cocoa into a bowl and stir to combine. Add the butter and mix with a fork until it looks like fine breadcrumbs. Stir in enough coffee to make a spreadable paste. Spread over the top and sides of the cake.