In the medium bowl, whisk together the sugar, cornstarch, coffee, and canela.
Slowly stir in the cream and milk.
Pour mixture into the heavy pan and add the cut vanilla bean. Slowly bring to a boil over medium heat. Watch it carefully so that it doesn't boil too fast, otherwise it will scorch.
As soon as it reaches a boil, turn heat back to medium-low and simmer for about 4 minutes, whisking constantly. Mixture will thicken.
Remove from heat and stir in the chopped chocolate and the butter until both are melted and fully incorporated.
Pour into the fondue pot and set over a tea light. Serve with dippers.