Chop the dark chocolate into small, even pieces to ensure it melts smoothly.

In a small saucepan, heat the heavy cream over medium-low heat until it begins to simmer. Do not let it boil.

Reduce the heat to low and add the chopped chocolate, stirring continuously until completely melted and smooth.

Add the butter, sugar (if using), vanilla extract, and a pinch of salt. Stir until everything is well combined and the mixture is glossy.

Transfer the chocolate mixture to a fondue pot or a heatproof serving bowl. Keep warm over a low flame or tea light.

Arrange the assorted dippers on a platter. Serve immediately with skewers or fondue forks for dipping.