You will need 4 1/2 times this recipe to cover our entire Truffle Cake.
Place chocolate in large heatproof bowl. Bring cream to a boil in heavy-bottom saucepan over medium-high heat; pour directly over chocolate. Allow to sit 10 minutes, then use a rubber spatula to stir chocolate and cream until combined.
Pour mixture into shallow dish; refrigerate until set, about 30 minutes.
Using 1/2-ounce ice-cream scoop, form balls from mixture; place on parchment-lined rimmed baking sheet. Refrigerate until firm. Remove from refrigerator; working quickly, roll each truffle between your hands to form a smooth ball; toss truffles in assorted cocoa powders. If truffles become too soft to handle, chill again until firm.
This recipe can be doubled.