Begin by chopping the dark chocolate into small, uniform pieces and placing them in a heatproof bowl.
In a small saucepan, heat the heavy cream over medium heat until it just starts to simmer. Be careful not to let it boil.
Pour the hot cream over the chopped chocolate. Let it sit for a minute to soften the chocolate.
Gently stir the mixture until all the chocolate is melted and the mixture is smooth and glossy.
Once the chocolate and cream are well combined, add the chocolate liqueur to the mixture and stir until fully incorporated.
Cover the bowl with plastic wrap and let it chill in the refrigerator for at least 2 hours, or until the mixture is firm enough to handle.
Once chilled, line a baking sheet with parchment paper. Using a spoon or a small scoop, scoop out portions of the chocolate mixture and roll them into small balls with your hands. Place the balls on the prepared baking sheet.
If desired, roll the truffles in cocoa powder, chopped nuts, sprinkles, or powdered sugar to coat them. Or, dip them in melted chocolate and let them set at room temperature. You can also leave them plain if you prefer.
Once all the truffles are coated, return them to the refrigerator to firm up for another 30 minutes to an hour.
Once firm, transfer the truffles to an airtight container and store them in the refrigerator until ready to serve.
