Preheat oven to 325 degrees. Assemble a 9-inch spring form pan with the raised side of the bottom facing down.
In a blender, pulse cookies until finely ground. Add butter, and pulse to moisten. Transfer to prepared pan, and press crumbs firmly and evenly into the bottom. Place pan on a rimmed baking sheet; bake 10 minutes, and set aside.
In a large bowl, add cream cheese, sugar, and salt; blend until smooth with electric mixer. Add eggs, then sour cream, and finally chocolate; blend filling until smooth, scraping down sides of bowl as needed. This is where I separated part of the filling and added the melted milk chocolate to 1/2 of the filling.
Pour filling onto crust, and bake just until set, 1 hour. Turn oven off, and let cheesecake sit 1 hour in oven, without opening (this helps prevent cracking).
Run a thin knife around the edge of the pan (this helps prevent cracking, too); leave in pan, and cool completely on wire rack. Cover loosely and refrigerate, at least 6 hours or up to overnight.
Unmold cheesecake. Spread ganache in center of cheesecake (IF USING) let set before serving.