In a medium heatproof bowl, add chopped chocolate and butter. In a small saucepan over medium heat, heat heavy cream until just simmering. Pour heavy cream over chocolate and let sit 5 minutes. Whisk until smooth. Refrigerate until firm, about 1 hour.
Line a large baking sheet with parchment paper. Using a small cookie scoop, scoop ganache and roll into smooth balls and place on prepared baking sheet. Refrigerate again until firm, about 30 minutes more.
Place cocoa powder in a small bowl and roll truffles in cocoa powder. Refrigerate until ready to serve.
For chocolate dipped truffles: Place melted chocolate in a small bowl and dip truffles in chocolate. Sprinkle with flaky sea salt or crushed candy canes. Refrigerate until hardened.
