Melt chocolate in cream in a medium, heavy-bottomed saucepan over medium-low heat, stirring constantly with a wooden spoon until smooth. Pour chocolate into a bowl and let cool at room temperature until thick enough to scoop with a spoon, 1 to 2 hours. (To speed process, refrigerate for 30 minutes, but do not let it get hard.)
Put cocoa in a bowl. Using a regular teaspoon, scoop about 1 Tbsp. cooled chocolate and roll between palms to form a 1-inch ball. Place ball in cocoa and roll until thoroughly coated. Repeat with remaining chocolate mixture.