Chop the dark chocolate into small pieces and place it in a heatproof bowl.
In a small saucepan, heat the heavy cream over medium heat until it starts to simmer.
Pour the hot cream over the chopped chocolate and let it sit for 2-3 minutes.
Add the unsalted butter to the chocolate mixture.
Stir gently until the chocolate and butter are fully melted and smooth.
Allow the mixture to cool to room temperature.
Cover the bowl and refrigerate for about 1 hour, or until firm.
Using a melon baller or small scoop, scoop out portions of the chocolate mixture.
Roll each portion into a ball using your hands.
Roll the truffles in cocoa powder, chopped nuts, or sprinkles to coat.