Place chocolate in a large bowl, or in the bowl of a stand mixer. Pour the cream into a saucepan, and bring to the boil. As soon as the cream boils up to the top of the pan, quickly remove it from the heat, and pour it over the chocolate. Let stand for a minute or two, then stir with a whisk, or use the paddle attachment for the mixer, to mix until smooth. Be sure to scrape the bottom of the bowl occasionally. Stir in the vanilla until well blended.
Place a piece of cling film directly on the surface, and allow to cool at room temperature, or in the fridge.