Preheat the oven to 180 degrees/160degrees fan. Grease a 20cm round cake tin (ideally a loose bottomed one but it doesn't really matter)
Place the cocoa and coffee granules (if using) into a cup and add enough hot water to make a smooth, thick paste
Put the butter/marg and sugar into a large bowl and whisk with an electric whisk for approx. 1 minute
Add the eggs, syrup, milk and cocoa paste and whisk until combined.
Add the flour and carefully mix in. Once incorporated whisk for a further minute or two
Place the mixture into the prepared tin, smooth and scatter the chocolate (and toffee pieces if using) on the top
Gently push the chocolate (and toffee if using) into the mixture - not too far or it will sink right to the bottom!
Cook the cake for 40-50 minutes until the top springs back when you press it lightly
Cool in the tin for 5 mins then turn out and leave to cool on a wire rack
Whilst cooling, make the icing by heating the chocolate, toffees (if using), butter/marg and milk in a saucepan over a low heat, stirring occationally.
Once melted add the icing sugar to the mixture and leave to cool
Spread the cooled icing on the cooled cake and decorate however takes your fancy...