Add the heavy cream and dark or bittersweet chocolate to a microwave-safe 2 quart bowl. Heat on HIGH for 3 minutes then let stand for 5 minutes. After 5 minutes, use a whisk to slowly stir the ganache in a circular pattern in one direction until it becomes shiny, about 3 minutes. Do not BEAT the ganache, just slowly stir it. Don't worry, it'll come together. Let the ganache stand for 15 minutes at room temperature, stirring once or twice. Pour the finished ganache over the peanut butter filling. Shake the pie gently from side to side to distribute the ganache evenly. Return the pie to the freezer until the ganache is firmed up.