On high power, heat heavy cream in the microwave for 1-2 minutes, until very hot and simmering, but not boiling.
While cream is heating, break chocolate into pieces, and put in a mixing bowl.
Pour hot cream over chocolate in bowl, and allow to stand for 5 minutes. Then stir until all pieces are melted and ganache is smooth. Allow to cool to room temperature.
Pour cooled ganache over pudding layer of cake, and spread, using an offset spatula.
Refrigerate entire cake at least 2 hours or, preferably, overnight, and serve cake cold.