Preheat your oven to 350F and lightly oil or line a 9 inch springform cake dish with parchment.

In a large mixing bowl, whisk together the flour, cocoa powder, baking powder, baking soda, salt, and cinnamon.

In another mixing bowl, whisk together the syrup, water, oil, and vinegar. Add the wet ingredients to the dry ingredients and whisk to combine thoroughly, but it's OK if there are a few small clumps. Fold half of the pear into the cake, then pour the batter into the pan. Top with the remaining pear and the chocolate. If you like, sprinkle a tablespoon of sugar over the top of the cake.

Transfer the cake to the oven and bake for 45 minutes, or until the top is rounded and set. Remove it from the oven. Allow it to cool for a whole hour, then you can release it from the springform pan. I recommend allowing it to cool for another couple hours before slicing: the dark chocolate will be very melty at first, and it's better to give it some time! Enjoy.