Finely chop the dark chocolate and place it in a heatproof bowl. Heat heavy cream in a saucepan over medium heat until just boiling. Pour hot cream over chocolate and let sit for 2 minutes before stirring until smooth.

Add unsalted butter to the chocolate mixture and stir until glossy. Optionally add flavor extracts.

Cover the bowl with plastic wrap and chill in the refrigerator for about 2 hours or until firm enough to scoop.

Use a melon baller or small cookie scoop to portion out small balls of chocolate. Roll quickly between palms into smooth truffles.

Roll each truffle in cocoa powder until fully coated, or use crushed nuts for variety.

Serve chilled on a platter or store in an airtight container.