Chop the chocolate finely and place it in a heatproof bowl so it melts evenly.
Heat the heavy cream in a small saucepan until it just begins to simmer; do not boil.
Pour the hot cream over the chopped chocolate and let sit 1–2 minutes to soften the chocolate.
Gently stir the mixture from the center until a smooth, glossy ganache forms.
Stir in the butter, vanilla (if using), and a pinch of salt until fully incorporated.
Cover the ganache and chill in the refrigerator until firm enough to scoop, about 1.5–2 hours.
Use a spoon or melon baller to portion ganache into small mounds.
Quickly roll each portion between your palms to form smooth balls, working fast to avoid melting.
Roll truffles in cocoa powder, chopped nuts, or dip in melted (tempered) chocolate for a shell.
Place finished truffles on parchment and chill 10–15 minutes to set; bring to room temperature briefly before serving.