Step 1: Preheat your oven to 350°F (175°C). Lightly grease a 9-inch springform pan. Wrap the bottom and sides of the springform pan with heavy-duty aluminum foil to prevent any water bath leakage (if using, otherwise for easier handling).
Step 2: For the crust, combine chocolate cookie crumbs and ¼ cup granulated sugar in a medium bowl. Pour in the melted butter and mix until crumbs are thoroughly moistened. Press the mixture evenly into the bottom of the prepared springform pan. Bake for 8-10 minutes, then remove and let cool slightly.
Step 3: Reduce oven temperature to 325°F (160°C).
Step 4: In a large mixing bowl, beat the softened cream cheese with 1½ cups granulated sugar until smooth and creamy, scraping down the sides of the bowl as needed.
Step 5: Gradually beat in the cocoa powder until fully incorporated and no streaks remain.
Step 6: Add the eggs one at a time, beating on low speed just until each egg is combined. Do not overmix.
Step 7: Stir in the sour cream and 1 teaspoon vanilla extract until just blended.
Step 8: Pour the cheesecake filling over the cooled crust in the springform pan. If using a water bath, carefully place the foil-wrapped springform pan into a larger roasting pan, and add hot water to the roasting pan until it reaches halfway up the sides of the springform pan.
Step 9: Bake for 55-65 minutes, or until the edges are set and the center slightly jiggles when gently shaken. Turn off the oven, crack the door open, and let the cheesecake cool in the oven for 1 hour.
Step 10: Remove the cheesecake from the oven and water bath (if used), unwrap the foil, and let cool completely on a wire rack. Once cool, cover loosely with plastic wrap and refrigerate for at least 4-6 hours, or preferably overnight.
Step 11: Once chilled, carefully remove the sides of the springform pan. Spread the cherry pie filling evenly over the top of the cheesecake.
Step 12: For the whipped cream topping, in a large, very cold mixing bowl, beat the heavy cream, powdered sugar, and ½ teaspoon vanilla extract on high speed until stiff peaks form.
Step 13: Pipe or spread the whipped cream around the edge of the cheesecake, or completely cover the cherry topping. Garnish with chocolate shavings or grated chocolate before serving.