To make the chocolate cake

1. Preheat oven to 350°F (176°C). Line a 9-inch (23cm) springform pan with parchment paper in the bottom and grease the sides.
2. In a medium sized bowl, combine the flour, sugar, cocoa, baking soda, baking powder and salt. Whisk until well combined.
3. In another medium sized bowl, combine the milk, vegetable oil, vanilla extract and egg white. Whisk until well combined.
4. Add the dry ingredients to the wet ingredients and whisk together until well combined.
5. Add the water and whisk until well combined. Batter will be thin.
6. Pour the batter into the springform pan and bake for 12-15 minutes, or until a toothpick inserted in the middle comes out with a few crumbs.
7. Remove cake from the pan and set aside on a cooling rack to cool. Wash the springform pan for use again later.

To make the Oreo cheesecake filling

1. While the cake is cooling, make the cheesecake filling. Add the chocolate chips to a medium sized bowl.
2. Heat the heavy whipping cream until it begins to boil, then pour it over the chocolate chips. Allow the mixture to sit for 3-4 minutes, then whisk until smooth. Set aside.
3. In a large mixer bowl, add the cream cheese, sugar and flour and beat on low speed until completely combined and smooth. Be sure to use low speed to reduce the amount of air added to the batter, which can cause cracks. Scrape down the sides of the bowl.
4. Add the sour cream and vanilla extract mix on low speed until well combined.
5. Add the eggs one at a time, mixing slowly to combine after each addition. Scrape down the sides of the bowl as needed to make sure everything is well combined.
6. Reduce the oven temperature to 300°F (148°C). Re-line the bottom of the 9 inch springform pan with parchment paper and spray the sides with non-stick spray. You want to be sure it’s well done so that they cheesecake doesn’t stick to the sides after baking. Prepare the pan for a water bath by wrapping the outside of the pan with aluminum foil. Here’s how I like to prepare my pans for a water bath to prevent leaking.
7. Reset the springform pan edges around the cooled chocolate cake, then pour the melted chocolate mixture on top of the cake. Spread it into an even layer.
8. Add the about 1/3 of the cheesecake filling to the pan and spread into an even layer. Top the filling with 10-12 Oreos (leave them whole).
9. Add another 1/3 of the cheesecake filling and spread into an even layer. Top the filling with another 7-8 Oreos, trying to offset their position from the ones on the first layer.
10. Add the remaining 1/3 of the filling, spread into an even layer, then top with another 10-12 Oreos. The Oreos will sit on top of the cheesecake.
11. Place the springform pan inside another larger pan. Fill the outside pan with enough warm water to go about halfway up the sides of the springform pan. The water should not go above the top edge of the aluminum foil on the springform pan.
12. Bake the cheesecake for 45 minutes. The center should be set, but still jiggly.
13. Turn off the oven and leave the door closed for 20 minutes. The cheesecake will continue to cook, but slowly begin to cool as well.
14. Crack the door of the oven for 30 minutes to allow the cheesecake to continue to cool slowly. This process helps prevent cracking.
15. Remove the cheesecake from the oven and water bath wrapping (leave it in the springform pan) and refrigerate until firm, 5-6 hours or overnight.

To make the Oreo mousse

1. To make the Oreo mousse, add the white chocolate chips and 2 tbsp (30ml) of heavy whipping cream to a small bowl. Microwave in 10 second increments until melted and smooth. Set aside to cool to about room temperature.
2. Whip remaining 1 cup (240ml) of heavy whipping cream, powdered sugar and vanilla extract in a large mixer bowl fitted with the whisk attachment until stiff peaks form.
   25. Carefully fold about 1/3 of the whipped cream into the cooled white chocolate mixture until combined.
3. Fold in the remaining whipped cream until well combined, then add the chopped Oreos – crumbs and all.
4. Spoon the Oreo mousse on top of the cooled cheesecake and spread into an even layer. Place the cheesecake back in the fridge until the mousse layer is cold and firm, 2-3 hours.
5. When the mousse layer is cold and firm, remove the cheesecake from the springform pan.

To finish off the cheesecake

1. To make the frosting, beat the butter until smooth.
2. Add the melted chocolate and mix until smooth and well combined.
3. Slowly add the powdered sugar and salt, mixing until smooth and well combined.
4. Add 4-5 tablespoons of cream, as needed, to get the right consistency frosting.
5. Place the cheesecake on a serving plate and frost the edges with the chocolate frosting.
6. Combine the mini chocolate chips and crushed Oreos and press them into the frosting on the sides of the cake.
7. Pipe frosting onto the top of the cheesecake in a spiral, beginning from the middle of the cheesecake and piping towards the edge.
8. Use the remaining frosting to pipe swirls around the outer edge of the top of the cheesecake.
9. Sprinkle some of the remaining mini chocolate chips and Oreo crumbs on the top of the cheesecake, then garnish with a few Oreos.
10. Refrigerate the cheesecake until ready to serve. The frosting can get a bit firm, so I suggest leaving it out for about 45 minutes before serving to make it easier to slice. Cheesecake is best when well covered and eaten within 4-5 days.