Heat the heavy cream in a small saucepan over medium heat just until it begins to simmer. Do not boil.
Pour the hot cream over the chocolate chips in a bowl. Let it sit for a minute, then stir until the chocolate is completely melted and the mixture is smooth.
Pour the ganache over the peanut butter layer, spreading it out evenly. Return to the refrigerator to chill for at least 1 hour, or until the ganache is set.