Start by melting the 1 oz chocolate for the cheesecake in a microwave safe bowl, in the microwave on half power, stirring every 20 seconds. Once fully melted, set aside to cool.
Make the ganache. Heat the heavy cream in the microwave until warm, then add the chocolate and whisk until fully melted. Whisk in the erythritol then set aside.
Pour 1/2 cup heavy cream into the bowl of a stand mixer and using the whisk attachment, whip into firm peaks. Scrape out the whipped cream into a separate bowl and set aside.
Using the stand mixer with paddle attachment, whip the cream cheese until all the lumps are gone. Scrape the bowl. Sift in the erythritol - very important, otherwise it will be super clumpy - and whip again. Add the sour cream, vanilla, salt and mix until just combined, then fold in the whipped cream.
Scoop out half of the cheesecake mixture into a separate bowl and set aside. Sift the cocoa powder into the remaining half and mix in well. With the machine on low speed, slowly pour in the melted chocolate until fully combined, then scrape the chocolate cheesecake into a bowl.
Mix the peanut butter into the cheesecake that had been taken out before the remainder was turned into chocolate cheesecake.