Chop the dark chocolate into small pieces and place it in a bowl.
In a saucepan, heat the heavy cream until it just begins to simmer.
Pour the hot cream over the chopped chocolate and let it sit for a minute.
Stir gently until the chocolate is completely melted and smooth.
Add vanilla extract and sea salt, stirring to combine.
Cover the mixture and refrigerate for about 1 hour until firm.
Once chilled, use a melon baller or spoon to scoop out small portions.
Roll each portion into a ball between your hands.
In a shallow dish, combine cocoa powder and powdered sugar.
Roll each truffle in the cocoa mixture until fully coated.