Preheat the oven to 350 degrees.
Over medium heat, add the sugar in a small saucepan. Stir constantly until golden brown and melted. Once done, pour the melted sugar into the bottom of an 8-inch pan and coat it evenly by tilting the pan from side to side. Set it aside while preparing the rest of the flan.
Whisk in the chocolate with the evaporated milk and melt it in a microwave for 30 seconds at a time. Remember to stir the milk and chocolate every 30 seconds until completely incorporated together. If you don't have a microwave, place the chopped chocolate on top of a double boiler over lightly simmering water.
Combine the chocolate you've just prepared with sweetened condensed milk, cinnamon, and vanilla in a bowl. Mix together with a whisk while adding the eggs one at a time. You can likewise use a blender or an electric whisk to combine the ingredients thoroughly.
Pour the mixture into the pan with the caramel you've prepared beforehand.
Bake the flan for about 50 minutes to an hour or until a toothpick comes out clean when inserted in the middle of the flan.
Once cooked, allow the flan to cool for 30 minutes before placing it inside your refrigerator for up to 5 hours.
Before flipping your flan on a serving plate, run a knife around the perimeter of the pan so it'll slide out easily. Place it back in the fridge or serve immediately!