Chop the dark chocolate and butter into small pieces.
In a small pot, melt the dark chocolate and butter over medium heat.
Pour the heavy cream into a bowl and whip it to about 70% stiff peaks using a whisk.
Let the melted chocolate and butter cool slightly, then fold them into the whipped cream.
Transfer the well-mixed chocolate cream into a container and chill in the refrigerator for about 1 hour.