Melt the chocolate over a bain marie or in the microwave in 30 second intervals, mixing after each interval.
Pour the cream and sugar into a pot and stir constantly over medium heat until the sugar is completely dissolves and steam comes out of the cream. Don't let it come to a boil or you could burn the chocolate, we just need it to steam.
Pour the cream onto the melted chocolate and mix with a spatula at the center of the bowl in small circles. You don't have to make large mixing motions; you'll see how the ganache comes together on its own.
Pour the ganache onto the base of the tart and spread it out.
Take the tart to the fridge for at least 6 hours or ideally overnight.