Chop the dark chocolate into small pieces and place in a heatproof bowl.

In a small saucepan, heat the heavy cream and butter over medium heat until it just begins to simmer. Do not boil.

Pour the hot cream mixture over the chopped chocolate. Let it sit for 1 minute, then stir until smooth and fully melted.

Stir in the champagne until well combined. The mixture should be glossy and smooth.

Cover the bowl with plastic wrap and refrigerate for at least 2 hours, or until firm enough to scoop.

Once chilled, use a small scoop or spoon to form the mixture into 1-inch balls. Roll quickly between your palms to smooth.

Roll each truffle in cocoa powder or powdered sugar until fully coated. Place on a parchment-lined tray.

Refrigerate the truffles for another 30 minutes to set before serving.