I added about 1/4 cup (didn't measure, actually) semi-sweet chocolate chips. The flavor was very nice and chocolatey. I also reduced the brown sugar to 1/2 cup. The cake ended up floating on a very soupy layer. I don't know if the smaller amount of brown sugar was the cause, but next time I will use less coffee--maybe a scant cup--along with the lower amount of brown sugar. All-in-all, great flavor, even with less sugar, but still needs some tweaking to get a thicker sauce.