In a bowl, whisk together sugar and cornstarch to blend.

Slowly whisk in the cream, then the milk, coffee, cinnamon, and vanilla bean.

Pour the mixture into a stainless steel saucepan and gently bring to a boil over medium low heat.

Cook, whisking constantly until thickened, about 4 minutes.

Remove the pan from the heat and whisk in the chocolate and butter until melted.

Pour through a fine mesh sieve into a large bowl and discard any solids

Pour into a warmed fondue pot and serve immediately with assorted dippers.