I think the "sour" part of sourdough is a misnomer. Yes, wild-fermented bread has a different flavor than packaged-yeast bread, but it's a subtle tang that matches well with many flavors. Like chocolate.
I've made this bread a few times, and it's got a subtle sweetness throughout combined with strong chocolate flavor. This week's is particularly chocolaty, probably because I used more than usual. (Despite the fact that it's made with Nestle chocolate chips instead of my usual Ghirardelli.)
There has been controversy in the past over whether to melt the chocolate and mix into the dough, or to have whole chips throughout. This time, I didn't quite melt the chocolate fully, so there were a few bits of pure chocolate mixed in a chocolaty dough. I think that's the way to go. 4 out of 5 stars.