Place the chocolate it in a heat-safe bowl.
Heat the heavy cream in a small saucepan over medium-low heat until steaming and small bubbles form around the edges. Do not boil.
Pour the warm cream over the chopped chocolate. Add the butter and sea salt. Let sit for 2 minutes.
Gently stir until the chocolate is fully melted and smooth. Stir in the vanilla extract.
Cover and refrigerate for 1–2 hours, or until the mixture is firm enough to scoop.
Scoop the truffle mixture and roll into balls using your hands.
Roll each truffle in cocoa powder until coated.
Refrigerate for 10–15 minutes before serving.