Place the chopped chocolate in a medium heat-proof bowl and set aside.
In a small saucepan, heat the heavy cream and butter over medium heat until it just begins to simmer. Remove from heat immediately.
Pour the hot cream mixture over the chocolate and let it sit for 2 minutes. Then stir gently until smooth and completely melted.
Stir in the 3 tablespoons cocoa powder, powdered sweetener, vanilla extract, cinnamon, and salt until well combined.
Cover the bowl and refrigerate for 2-3 hours, or until firm enough to scoop.
Place the remaining cocoa powder in a shallow dish. Using a small cookie scoop or spoon, form the chocolate mixture into 1-inch balls.
Roll each truffle in the cocoa powder until evenly coated. Store in an airtight container in the refrigerator for up to 2 weeks or freeze for up to 3 months.