Place the finely chopped chocolate in a heatproof bowl. In a small saucepan, heat the heavy cream over medium heat until it just begins to simmer (do not boil).
Pour the hot cream over the chocolate. Let it sit for 2 minutes, then gently stir until smooth. Add the butter and stir until fully incorporated.
Cover the bowl with plastic wrap and refrigerate for at least 2 hours, or until the mixture is firm enough to scoop.
Line a baking sheet with parchment paper. Using a small melon baller or teaspoon, scoop the chocolate mixture and roll into 1-inch balls. Place on the prepared sheet.
Roll each truffle in desired coating (cocoa powder, nuts, etc.) or dip in melted chocolate for a hard shell. Refrigerate until firm, about 30 minutes.
Store in an airtight container in the refrigerator for up to 2 weeks. Serve at room temperature.
Tips
For best flavor, use high-quality chocolate.
To make white or milk chocolate truffles, substitute the dark chocolate accordingly.
Truffles can be frozen for up to 3 months; thaw in the refrigerator before serving.