01 - Place chopped dark chocolate in a heatproof bowl.
02 - Warm heavy cream in a small saucepan over medium heat until it just begins to simmer; avoid boiling.
03 - Pour hot cream evenly over the chocolate and let sit undisturbed for 2 minutes to melt.
04 - Whisk the mixture gently in small circular motions from the center outward until smooth and glossy.
05 - If desired, add butter, vanilla extract, and salt, stirring gently until fully melted and combined.
06 - Use warm as glaze, or cool to room temperature for spreading or frosting. For truffles, chill until firm before shaping.