Make the Chocolate Cake Layer
1-Preheat the oven to 350°F: Preheat the oven to 350°F. Grease a 9-inch cake pan with baking spray. Line the bottom with parchment paper and spray the paper, too.
2-Melt the chocolate and butter in a: Melt the chocolate and butter in a small microwave-safe bowl, stirring every 30 seconds, until completely melted and smooth. Set aside to cool slightly.
3-In a separate bowl, whisk the eggs: In a separate bowl, whisk the eggs and sugar until well combined. Whisk in the melted chocolate mixture, cocoa powder, vanilla extract, and salt.
4-Sift in the flour and baking powder: Sift in the flour and baking powder and stir with a spatula just until combined.
5-Pour the cake batter into the prepared: Pour the cake batter into the prepared pan and bake for 18-20 minutes, or until the cake is set.
6-Cool in the pan for 5-10 minutes,: Cool in the pan for 5-10 minutes, then transfer to a rack to cool completely. Once cooled, wrap tightly in plastic wrap and set aside until ready to assemble.

Make the Oreo Cheesecake
7-Preheat the oven to 325°F: Preheat the oven to 325°F. Grease a 9-inch springform pan and line the bottom with parchment paper.
8-In a large mixing bowl, beat the: In a large mixing bowl, beat the cream cheese, sugar, and flour until smooth and creamy. Scrape down the sides and bottom of the bowl as needed.
9-Add the sour cream and vanilla extract: Add the sour cream and vanilla extract and mix on low speed until combined.
10-Add the eggs and egg yolk one: Add the eggs and egg yolk one at a time, mixing on low speed just until combined after each addition. Do not overmix.
11-Pour about 1/3 of the cheesecake batter: Pour about 1/3 of the cheesecake batter into the prepared pan. Arrange 10 Oreo cookies over the batter. Spread the remaining cheesecake batter over the Oreos, then add more Oreo cookies on top and gently press them into the batter. It is fine if the top layer of batter is thin in some places.
12-Wrap the outside of the springform pan: Wrap the outside of the springform pan with aluminum foil to help prevent water from leaking in. Place the springform pan in the roasting pan with hot water. The water should not go above the foil.
13-Bake for 55-65 minutes, or until the: Bake for 55-65 minutes, or until the edges are set and the center is still slightly jiggly.
14-Turn off the oven, crack the oven: Turn off the oven, crack the oven door open, and leave the cheesecake inside for 45-60 minutes.
15-Remove from the oven and water bath,: Remove from the oven and water bath, then cool to room temperature. Refrigerate for at least 1-2 hours, or until completely cold and firm enough to handle. To speed this up, you can chill it briefly in the freezer after it has cooled to room temperature.

Make the Chocolate Ganache Frosting
16-Place the finely chopped chocolate in a: Place the finely chopped chocolate in a large heatproof bowl.
17-Heat the heavy cream until it just: Heat the heavy cream until it just begins to simmer. Do not boil it.
18-Pour the hot cream over the chopped: Pour the hot cream over the chopped chocolate, cover, and let it sit for 2-3 minutes. Gently stir until the chocolate is completely melted and smooth. Stir in corn syrup. If needed, microwave for a few seconds and stir again until smooth.
19-Let the ganache cool until thick: Let the ganache cool until thick. You can refrigerate it to speed up the process, but stir occasionally so it cools evenly.
20-When the ganache is thick and ready: When the ganache is thick and ready to use, transfer it to a mixing bowl and beat with the whisk attachment until light, fluffy, and spreadable. If the ganache becomes too firm in the fridge, let it sit at room temperature for 15-20 minutes before whipping.
21-If you prefer a sweeter frosting, add: If you prefer a sweeter frosting, add powdered sugar to taste.

Make the Oreo White Chocolate Mousse
22-Melt the white chocolate with 2 Tablespoons: Melt the white chocolate with 2 Tablespoons heavy cream in the microwave, stirring every 20-30 seconds until smooth. Set aside to cool to room temperature.
23-In a separate bowl, beat 1 cup: In a separate bowl, beat 1 cup cold heavy whipping cream and powdered sugar until stiff peaks form.
24-Add a small amount of the whipped: Add a small amount of the whipped cream to the cooled, melted white chocolate and stir to lighten it.
25-Gently fold the white chocolate mixture back: Gently fold the white chocolate mixture back into the remaining whipped cream.
26-Fold in the crushed Oreo cookies: Fold in the crushed Oreo cookies. Refrigerate until ready to assemble.

Assemble the Cheesecake
27-Place the chocolate cake layer on a: Place the chocolate cake layer on a serving plate or cake board.
28-Spread a thin layer of whipped chocolate: Spread a thin layer of whipped chocolate ganache frosting over the cake layer. Carefully place the chilled Oreo cheesecake on top.
29-Spread the Oreo white chocolate mousse evenly: Spread the Oreo white chocolate mousse evenly over the cheesecake. Chill for 30-60 minutes, or until the mousse is firm enough to frost.
30-Reserve some ganache frosting for the piped: Reserve some ganache frosting for the piped decoration on top. Spread a thin, even layer of ganache frosting over the top and around the sides.
31-Mix the crushed Oreos and mini chocolate: Mix the crushed Oreos and mini chocolate chips in a small bowl. Press the mixture onto the sides of the cheesecake.
32-Transfer the reserved ganache frosting to a: Transfer the reserved ganache frosting to a piping bag fitted with a large round tip. Pipe the frosting in circles or a spiral pattern over the top to create a ridged Cheesecake Factory-style look.
33-Decorate the top with whole Oreo cookies: Decorate the top with whole Oreo cookies.
34-Refrigerate the cheesecake for at least 4: Refrigerate the cheesecake for at least 4 hours before slicing, preferably overnight. For cleaner slices, use a sharp knife and wipe it clean between each cut.