To Make the Chocolate Filling:

1. Place the chocolate, butter, and cinnamon in the top bowl of a double boiler. Heat the water, and melt the chocolate mixture until everything is melted and combined, stirring occasionally.
2. Set aside and allow to cool completely and thicken slightly, about 15-20 minutes.

To Assemble:

1. While the chocolate filling is cooling, line two 9-by-5-inch loaf pans with parchment paper, allowing 2 inches of overhang on each of the long sides. Spray with nonstick cooking spray.
2. Set the chilled brioche dough on a well-floured work surface. Cut the dough equally in half and set aside.
3. Roll out each portion of dough into a 16-inch square.
4. Using an offset spatula, spread half of the cooled chocolate filling in an even layer on each dough square, leaving a border of about 1/4 inch around the edge.
5. Starting at the edge nearest you, tightly roll up each dough square into a tight log, like a cinnamon roll. Finish with the seam on the bottom, touching the work surface.
6. Using a sharp knife, cut the logs in half across the entire length of the roll. Place the cut sides facing upwards.
7. Pinch the two halves together at one end, and twist the two pieces together to form a tight spiral, like a double-helix. Pinch the ends together.
8. Carefully transfer each loaf to the prepared pans. Proof at room temperature until doubled in size, about 45 minutes.

To Bake:

1. When the loaves are almost finished proofing, preheat the oven to 350°F.
2. Bake the loaves in the center of the oven for about 30-45 minutes, until puffed and well browned. Let cool slightly, then use the parchment paper to lift the them out of the pans and onto a cooling rack set over a sheet pan. Let cool for 10 minutes before cutting into slices. Enjoy warm, or cool completely.