Chop chocolate finely using a serrated knife, and place in a large heat-proof bowl.
In a medium saucepan, bring cream to a boil over medium-high heat; pour directly over chopped chocolate. Allow to sit 10 minutes; use a rubber spatula to gently stir chocolate and cream until combined. Allow to sit at room temperature until just thickened, about 15 minutes.
Pour ganache mixture into a shallow glass dish. Cover with plastic wrap, and refrigerate until mixture is very cold and set but still pliable, about 30 minutes.
Using a small spoon, scoop out ganache into 1-inch nuggets; place on a parchment-lined baking sheet. Chill for 10 minutes. Use fingertips to mold truffles into round shapes. Roll in cocoa powder to coat; chill in an airtight container until ready to serve.