1. Prepare the Red Velvet Cake Layers: A Moist and Flavorful Base

Preheat and Prep Pans: Preheat the oven to 325°F (160°C). Spray one 9-inch springform pan and one 8-inch round cake pan with nonstick spray. Line the bottom of each pan with a parchment paper round and spray again.

Tip: The parchment paper will ensure easy removal of the cake layers.

Combine Dry Ingredients: In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, baking powder, and salt.

Combine Wet Ingredients: In a separate bowl, whisk together the buttermilk, oil, eggs, hot water, and vanilla extract.

Add Food Coloring: Add the red food coloring to the wet ingredients and whisk until the color is evenly distributed.

Gradually Add Wet to Dry: With the mixer on low speed, gradually add the wet ingredients to the dry ingredients, scraping the bottom of the bowl with a rubber spatula as needed. Mix until just combined.

Divide and Bake: Divide the batter evenly between the prepared 9-inch springform pan and the 8-inch round cake pan. Bake for 25 to 30 minutes.

Check for Doneness: The cakes are done when a toothpick inserted into the center comes out with just a few moist crumbs attached.

Cool: Let the cakes cool in the pans for about 10 minutes before inverting them onto a wire rack to cool completely.

2. Make the Oreo Cheesecake Filling: A Creamy, Dreamy Center

Separate Oreos: Separate 10 Oreo cookies. Scrape the filling into a medium bowl and set aside.

Crush Oreo Wafers: Blend the 10 separated Oreo wafers in a food processor until they turn into fine crumbs. Set aside for the crust.

Beat Cream Cheese: Using a stand mixer fitted with a paddle attachment, beat the softened cream cheese on high speed for about 2 minutes until smooth and creamy. Scrape down the sides of the bowl as needed.

Incorporate Oreo Filling and Sugar: Add the reserved Oreo filling and the granulated sugar to the cream cheese. Beat on medium speed until well combined.

Add Thickening Agent: Add the cornstarch (or all-purpose flour) and mix until incorporated.

Add Sour Cream and Vanilla: Add the sour cream and vanilla extract, mixing on medium speed until smooth. Scrape down the bowl to ensure thorough mixing.

Incorporate Eggs: Add the eggs and the egg yolk one at a time, mixing on low speed until just combined after each addition.

Tip: Do not overmix once the eggs are added, as this can cause the cheesecake to crack during baking.

Fold in Chopped Oreos: Gently fold in the 15 chopped Oreo cookies using a rubber spatula.

3. Prepare the Oreo Crust in the Springform Pan:

Mix Crumbs and Butter: In the medium bowl, combine the crushed Oreo wafers with the melted butter until well combined.

Press into Pan: Press the mixture evenly and firmly into the bottom of the springform pan, forming an even crust.

4. Assemble and Bake the Cheesecake: Creating the Layered Masterpiece

Pour Filling: Pour the Oreo cheesecake filling over the cooled red velvet cake layer in the 9-inch springform pan. Smooth the top with a spatula.

Prepare Water Bath:

Method 1 (Cake Pan): Place the springform pan inside a 10-inch cake pan. Place the cake pan inside a large roasting pan. Fill the roasting pan with hot water, about halfway up the sides of the cake pan.

Method 2 (Aluminum Foil): Wrap the outside of the springform pan tightly with two layers of heavy-duty aluminum foil. Place the wrapped pan inside a large roasting pan. Fill the roasting pan with hot water, about halfway up the sides of the springform pan.

Bake: Carefully transfer the roasting pan with the cheesecake to the preheated oven. Bake for about 1 hour and 30 minutes.

Check for Doneness: The cheesecake is done when the edges are set and lightly golden, and the center still has a slight jiggle.

Cool in Oven: Turn off the oven, crack open the door, and let the cheesecake cool slowly inside for 30 minutes to 1 hour. This gradual cooling helps prevent cracking.

Cool at Room Temperature: Remove the cheesecake from the water bath and let it cool completely at room temperature on a wire rack.

Chill: Cover the cheesecake with foil or plastic wrap and chill in the refrigerator for at least 6 hours, or preferably overnight, to allow it to fully set.

5. Prepare the Ganache Topping: A Rich Chocolate Finish

Chop Chocolate: Finely chop the dark chocolate and place it in a heatproof bowl.

Heat Cream: In a small saucepan, heat the heavy cream over medium heat until it just begins to simmer.

Pour Over Chocolate: Pour the hot cream over the chopped chocolate. Let it sit undisturbed for about 1 minute.

Whisk Until Smooth: Gently whisk the chocolate and cream mixture until the chocolate is completely melted and the ganache is smooth and glossy.

6. Assemble and Decorate: The Final Touches

Remove Cheesecake from Pan: Once the cheesecake is fully chilled, carefully remove the sides of the springform pan.

Pour Ganache: Pour the warm (but not hot) ganache over the top of the chilled cheesecake, allowing it to drip down the sides if desired. Use a spatula to spread it evenly if needed.

Prepare Red Velvet Layer: Crumble the 8-inch round red velvet cake layer that was baked separately into fine crumbs.

Decorate Sides: Gently press the red velvet cake crumbs onto the sides of the cheesecake, creating a decorative border.

Pipe Frosting: If desired, use a piping bag fitted with a decorative tip to pipe swirls or rosettes of the store-bought cream cheese frosting on top of the ganache.

Garnish: Decorate the top of the cheesecake with the remaining 8 chopped Oreos.

Chill: Refrigerate the decorated cheesecake for at least 30 minutes to allow the ganache to set before serving.