Preheat the oven to 350°F.
In a mixing bowl, beat cream cheese, sugar, and cornstarch until smooth.
Add sour cream, vanilla, and melted chocolate, mixing until well combined.
Gradually add eggs and egg yolks, one at a time, mixing well after each addition.
Pour the batter into the prepared crust.
Place the springform pan in a larger roasting pan, then pour boiling water into the roasting pan to create a water bath.
Bake for 1 hour, then let it cool in the oven with the door cracked open.
Once cooled, refrigerate for at least 8 hours.