Step 1: Preheat the Oven

1. Preheat your oven to 325°F (160°C). Line an 8×8-inch baking pan with parchment paper, leaving some overhang for easy removal.

Step 2: Make the Crust

1. In a medium bowl, mix the chocolate cookie crumbs, melted butter, and sugar until well combined.
2. Press the mixture firmly into the bottom of the prepared baking pan to form an even layer. Bake for 10 minutes, then remove from the oven and let cool.

Step 3: Prepare the Cheesecake Filling

1. In a large mixing bowl, beat the softened cream cheese and sugar together until smooth and creamy.
2. Add the eggs, one at a time, mixing well after each addition. Then, mix in the vanilla extract, sour cream, and cocoa powder until fully combined.

Step 4: Bake the Cheesecake

1. Pour the cheesecake filling over the cooled crust and spread it evenly.
2. Bake in the preheated oven for 25-30 minutes, or until the center is set and the edges are lightly golden. Remove from the oven and let it cool to room temperature.

Step 5: Prepare the Cherry Topping

1. In a small saucepan over medium heat, combine the cherry pie filling with cornstarch and water (if using). Stir until the mixture thickens slightly, about 2-3 minutes.
2. Remove from heat and let cool slightly.

Step 6: Assemble and Chill

1. Once the cheesecake has cooled, spread the cherry topping evenly over the cheesecake layer.
2. Cover and refrigerate for at least 2 hours or until fully chilled and set.

Step 7: Serve

1. Use the parchment overhang to lift the cheesecake out of the pan. Cut into bars and serve chilled.