There are two ways to use coffee and chocolate together in cakes - one is to use a little coffee to deepen the flavour of the chocolate, which often means the coffee isn't detectable in the flavour, and the other is to use more coffee and less chocolate to make a cake which tastes of the coffee as much as the chocolate. The second is what I tried to do here. The flavour was successful, but the grated chocolate that I added to the batter disappeared during baking, so I didn't get the flecky appearance I was hoping for. I was worried that the very wet batter wouldn't support chocolate chips, but my grated chocolate was too fine and melted into the batter.
this Annie Bell recipe, which is the nearest I've come to getting the texture of a sponge cake, using oil instead of butter. In this case, I left out all the lemon flavouring and dissolved 3 teaspoons of instant coffee in the milk before mixing the batter. I then folded in 30g grated plain chocolate before baking.
For the topping I made my favourite chocolate fudge frosting - melt 175g plain chocolate and 30g butter over a low heat, then beat in 2 tablespoons golden syrup and 3 tablespoons milk, leave to cool but use while still spreadable - and finished off with a light sprinkle of 'cappuccino pearls'.
Note added 23rd March: At Baking Addict's suggestion I am entering this in the AlphaBakes Challenge, a new monthly baking challenge hosted alternately by The More Than Occasional Baker and Caroline Makes. Caroline is hosting this month and the letter M has been randomly chosen. M for Mocha, obviously!