Preheat the oven to 325°F / 163°C and mix the chocolate cookie crumbs with melted butter, then press into the bottom of a 9-inch springform pan.
Beat the cream cheese and sugar until smooth, then add the eggs one at a time, followed by vanilla extract and sour cream.
Divide the batter in half, fold the melted chocolate into one half, then pour the chocolate batter over the crust and spread evenly.
Carefully pour the vanilla batter over the chocolate layer and smooth the top.
Bake for 55 to 60 minutes until the edges are set but the center still jiggles slightly, then turn off the oven and let the cheesecake cool inside with the door cracked for 1 hour.
Refrigerate for at least 4 hours or overnight until fully chilled and firm before slicing.