Originally from Martha, I got the recipe for these from smitten kitchen. I saw a few warnings with the recipe, but went ahead anyway because they just sounded so good.
I will however warn anyone trying to make these of the troubles I ran into (that seem to be the same troubles as everyone else). First, the chocolate dough and pumpkin dough are not the same consistency. The chocolate dough is far too thick and this makes it impossible to create a proper swirl effect. Also the cooking time is not quite long enough, and after taking the pan out of the oven (clean toothpick inserted and all) and covering in decorative chocolate, when I went to cut into squares I was faced with a far too-gooey centre. I then had to put them back in the oven (goodbye decorative chocolate) and find now that the chocolate part of the brownie (at least) is very dry. I thought the hazelnuts were great and I added them and a few chocolate chips right into the batter as well -- they are brownies after all, go big or go home, right?
All in all they still taste pretty great and give a sense of the season too -- and obviously we are still going to eat them.