Preheat the oven to 350F. Thoroughly grease a large Bundt tin with butter, making sure to get into all the nooks and crannies.
In a medium sized bowl, whisk together the flour, the cocoa powder, the cinnamon, the baking powder, the bicarbonate of soda, and the salt until combined. Set this to one side.
In a large bowl or stand mixer, beat together the butter and the sugar for three to four minutes, until it is lighter in color and throughly creamed.
Beat in 2 of the eggs one at a time, and then the vanilla extract, and mix until the mixture is smooth.
Mix in half of the flour and cocoa mixture until it is combined, and then add the buttermilk and mix again, before adding the remaining half of the flour and cocoa mixture, to form a thick chocolate cake batter. Set this to one side.
In a large, clean bowl, add the three remaining eggs and whisk them with a balloon whisk for 30 seconds. Then add the cream cheese and mix until they are well combined and there are no lumps of cream cheese.
Pour in the sweetened, condensed milk and the evaporated milk, and scrape out the seeds from the vanilla pod and add these to the bowl. Add the salt and then whisk everything until a smooth, creamy liquid batter is formed.
To prepare the chocolate flan for baking, smear ¼ cup of caramel sauce around the base of the greased Bundt tin. Then transfer the thick chocolate batter to the Bundt tin, and gently smooth it out using the back of a spoon. Finally, transfer the flan batter to the bundt tin, carefully pouring it on top of the chocolate batter. Cover the top of the Bundt tin with foil and place it into the preheated oven in a Bain Marie, with water ideally coming two inches up the sides of the Bundt tin.
Cook the covered chocolate flan for 1 hour, until the chocolate base has risen, and a skewer comes out with just a few crumbs when inserted. Remove the chocolate flan from the oven and allow it to sit for one to two hours until cool, before carefully turning out onto a plate.
Slightly heat the remaining caramel sauce and drizzle it around the top of the chocolate flan, and decorate with chopped pecans if desired.