Line a baking sheet with a parchment paper.
Using a double boiler, melt the dark chocolate. Stir the chocolate occasionally with a rubber spatula.
Pour the melted chocolate on the prepared baking sheet.
Put the baking sheet into the freezer and let the chocolate set for at least 2 hours.
Meanwhile, while waiting for the chocolate to be set, make avocado mousse.
Peel the avocado and remove the pit,