Whilst the brioche dough is proofing, prepare the filling. For the cinnamon butter, combine cinnamon, sugar and butter and mix to form a paste. For the chocolate, chop the chocolate blocks into small rough chunks. Set the filling aside.
Once the dough has doubled its size, flatten the dough with a fist and then scrape the dough onto a lightly floured (clean!) surface.
Roll the dough out to a large rectangular sheet with a rolling pin. About 30cmx40cm/ 12inx16in.
Spread the cinnamon butter evenly across the dough with a large spoon.
Sprinkle chopped chocolates evenly across the dough.
Gently but tightly roll up the dough from the long side, from one end to the other.
Now, horizontally half the rolled dough with a knife (or a dough scraper) and gently plait.
Gently place the dough plait into a lightly buttered loaf tin. If necessary (if the plait is a little long), lightly push in the ends of the plaits so that it fit the loaf tin.
Cover the loaf tin with plastic film/cling wrap and proof the dough. Place in a warm area (but not directly in the sun), allow the dough to almost double in size, takes about 2.5 - 3 hours.
Once proofing is done, remove plastic film/cling wrap and bake at 180°C/360°F in the middle shelf of the oven for 30 minutes.
Allow loaf to cool for 5 minutes before transferring onto a cooling rack.
Dig in whilst it's still warm.