Finely chop the dark chocolate.
Heat the heavy cream in a saucepan.
Add the chocolate to the warmed cream and melt together.
Add room temperature butter and mix thoroughly.
Pour the chocolate mixture into a mold lined with parchment paper and smooth out the surface.
Chill in the refrigerator for at least 2 hours until set.
Remove from the mold and cut into bite-sized pieces.
Evenly sift cocoa powder over the chocolates.