Using a food processor, grind the chocolate sandwich cookies into crumbs. Stir in the melted butter. Press mixture tightly into the bottom of a greased 9" springform pan. Chill in the refrigerator while you work on the filling.
To make the filling:
Preheat oven to 300°F. Using a hand mixer or a stand mixer fitted with the paddle attachment, beat the cream cheese until smooth and creamy.
Add the sweetened condensed milk, melted chocolate, and sour cream and beat until combined, stopping to scrape the sides of the bowl as necessary.
Pour the filling into the prepared crust. Bake for 40-45 minutes, until filling is slightly firm. Cool cheesecake completely, then chill in the refrigerator for at least 6 hours.
To make the ganache:
In a microwave safe bowl or mug, heat heavy cream for about :45-:55. Cream should be hot but not scorching. Remove from the microwave and pour over chocolate chips. Let the mixture sit for 2 minutes before stirring.
Cool ganache completely, then spread on top of chilled cheesecake. Refrigerate for about 5 minutes, just to allow ganache to set before serving.
Notes
Be sure to use blocks (not the spreadable kind) of full-fat cream cheese.
It’s important to bring the cream cheese and sour cream to room temperature before mixing.