Chop the bittersweet chocolate and place it in a heatproof bowl.
Add the heavy cream and champagne to a small saucepan. Heat on medium until steaming, not boiling.
Pour the hot cream mixture over the chopped chocolate. Let it sit for 1 minute.
Stir slowly until smooth and shiny.
Add pistachio butter, butter, and salt. Stir until fully mixed.
Cover the bowl and chill for 1 to 2 hours, until firm but scoopable.
Use a cookie scoop to portion the ganache. Roll quickly into balls.
Place truffles on parchment paper and chill for 30 minutes.
Melt the coating chocolate gently using a double boiler or microwave.
Dip each truffle into melted chocolate. Let excess drip off.
Place back on parchment and sprinkle chopped pistachios on top.
Let the chocolate set fully before serving or storing.