In a medium-sized saucepan, heat the heavy cream over medium heat until it just begins to simmer.
Remove the pan from the heat and add the chopped chocolate and butter. Stir until the chocolate and butter are completely melted and the mixture is smooth.
Stir in the powdered erythritol, vanilla extract, and sea salt until well combined.
Transfer the mixture to a bowl and let it cool to room temperature.
Once the mixture has cooled, cover the bowl and place it in the refrigerator for 2-3 hours, or until the mixture is firm.
Using a melon baller or small spoon, scoop the mixture into small balls and roll them in the unsweetened cocoa powder until coated.
Store the truffles in an airtight container in the refrigerator for up to a week.