Create a double boiler. Fill a saucepan a little less than halfway with water and bring to a low boil on low heat. Place a bowl over the top of it, making sure the water never touches the bottom of the bowl.
Add the chocolate to the bowl and using a spoon or spatula stir until the chocolate has melted and is smooth.
Pour in the heavy cream. Continue to stir until it is fully incorporated and silky smooth.
Add the remaining ingredients except for the cocoa powder. Stir until combined.
Cover the bowl with plastic wrap and allow it to refrigerate for 2-3 hours to overnight.
Use a small scoop to form your truffles. Drop them into the cocoa powder and roll them until they are completely covered.
Keep the dark chocolate truffles stored in an airtight container in the refrigerator until ready to serve.