In another pan, combine the cream, sugar, and the vanilla bean. Bring this mixture to a boil over low heat, stirring constantly to prevent scorching. Once it reaches a boil, remove the pan from the heat, take out the vanilla bean, and stir in the milk-gelatin mixture until everything is well combined.
Prepare your serving vessels: you can use ramekins, molds, or cups. Rinse each one with ice-cold water, shaking out any excess, then fill them with the panna cotta mixture. Transfer them to the refrigerator and chill for several hours, or at least 3-4 hours, until the panna cotta is fully set and firm to the touch. Once set, you can turn them out onto a serving dish if desired.
While the panna cotta chills, prepare the chocolate ganache. In a double boiler, melt the chocolate bar until smooth. Once fully melted, slowly whisk in cream until the ganache reaches your desired consistency – it should be glossy and pourable.