I made the recipe posted in the link below:
Interestingly enough, after printing it out from here I realized that this recipe is from the Martha Stewart Baking Book. The only difference is that she has you use 2# chocolate, not 2 1/4#. I don't have any 9x5 pans, so I bought 3 of the 8x3 3/4 (or some such) and I already had one around the house. So, I divvied the dought and filling into fourths instead of thirds when making the loaves. This recipe makes a MOUNTAIN of chocolate babka. I've got three in the freezer now.
I don't know from authentic, but this is incredibly good tasting, VERY rich and buttery. I love the addition of the cinnamon to the chocolate. I think you could also drop out the cinnamon, reduce the amount of chocolate and add some walnuts and dried cherries and it would be delicious as well. If I had one complaint, it might be that this is, perhaps, too rich (gasp).
Thanks for posting the recipe!
(oh, and I skipped the streusel topping--it struck me as totally superfluous)