I saw this recipe and I had to try it. I used Trader Joe's 72% dark pound chocolate pound plus bar. (Some reading suggested that there is not a formal difference between "dark" and "bittersweet."
I had to beat the egg/sugar mixture for quite a while, and it never really reached the color/texture combo described. Perhaps the eggs were too old, but colorwise I'm no sure how brown sugar would ever let this be pale yellow.
Anyway. The results were good, but kind of too fudgelike for me. Very dense, but almost too dense, if that makes sense. I would prefer a little moist and cakey, perhaps, rather than simply solid. But perhaps they are so solid because the eggs didn't go as planned. Hard to know. I think, overall, I prefer cocoa-based brownies. They are less work, too.