In a large bowl, mix the cream cheese, sugar and cornstarch together with a hand mixer on medium speed until smooth and free of lumps, about 2 minutes.
24 oz (680 g) cream cheese, softened at room temperature, 3/4 cup (150 g) granulated white sugar, 1/2 tbsp (4 g) cornstarch
Add in the melted milk chocolate, sour cream and vanilla and mix on medium-low speed just until combined.
6 oz (170 g) milk chocolate bars, melted and slightly cooled, 1/4 cup (62 g) sour cream, at room temperature, 2 tsp vanilla
Add the eggs to the cheesecake mixture and mix on medium-low speed just until combined.
3 eggs, at room temperature
Pour the cheesecake batter into the prepared pan with the crust. Bake for 39-42 minutes, just until the center only has a slight jiggle. Then turn the oven off and prop the oven door open for 10 minutes using a wooden utensil.
Remove the cheesecake from the oven and allow it to cool completely in the pan on a wire rack. Then transfer it to the fridge and allow it to chill in the fridge for 6 hours, or until completely cold. (I usually bake it the night before and allow it to chill overnight.)