For the Brownie: 

1. Preheat the oven to 350°F. Line the bottom of a 9-inch springform pan with parchment paper.
2. In a medium-sized bowl, combine the brownie mix, with the ingredients listed on the box. Stir until the batter is well combined and there are no dry ingredients left.
3. Pour the batter into the springform pan and spread evenly.
4. Bake at 350°F for 30-35 minutes until the center is baked but still slightly fudgy.
5. Allow the brownie to cool completely.

For the Oreo Mousse: 

1. In a microwave-safe bowl, microwave the white chocolate at 50% power in 30 second increments until the chocolate is melted, stirring occasionally.
2. Once melted, stir until smooth. Set aside to cool.
3. In a small dish, combine 1 tablespoon of cold water with 1 teaspoon gelatin. Sprinkle the gelatin over the cold water and allow it to set to a solid.
4. Microwave the gelatin for 8-10 seconds until it turns back to a liquid, watch closely.
5. To prepare the whipped cream, place the metal mixing bowl and whisk in the freezer for 5-10 minutes.
6. Pour the heavy whipping cream into the chilled bowl and use an electric mixer to beat the heavy cream on medium-high speed until the cream starts to thicken.
7. Slowly add the powdered sugar and liquid gelatin and continue beating on high speed until stiff peaks form. Set the whipped cream aside.
8. Beat the softened cream cheese on medium-high speed for 2-3 minutes, until the cream cheese is free of lumps, scraping the bowl occasionally.
9. Next, add the melted chocolate and mix thoroughly into the cream cheese mixture.
10. Finally, fold the prepared whipped cream into the cream cheese mixture and stir gently until the mixture is well combined.
11. Fold in the crushed Oreos, then spread the mousse over the cooled brownie (in the springform pan).

For the Chocolate Chip Cookie Mousse:

1. Prepare another batch of gelatin, sprinkling the powdered gelatin over the cold water and allow to set. Once set, melt in the microwave for about 10 seconds.
2. Prepare a second batch of whipped cream (as instructed above). Place the mixing bowl and whisk in the freezer for 5-10 minutes.
3. Pour the heavy whipping cream into the chilled bowl and use an electric mixer to beat the heavy cream on medium-high speed until the cream starts to thicken.
4. Slowly add the powdered sugar and gelatin and continue beating on high speed until stiff peaks form.
5. Fold the crushed chocolate chip cookies into the whipped cream and spread over the layer of Oreo cheesecake.
6. Cover with aluminum foil and refrigerate for 3-4 hours to allow the layers to set.

For the Topping:

1. Prior to serving, prepare another batch of whipped cream as instructed above.
2. Pour the heavy whipping cream into the chilled bowl and use an electric mixer to beat the heavy cream on medium-high speed until the cream gets bubbly.
3. Slowly add the powdered sugar and continue beating on high speed until stiff peaks form.
4. Pipe the top of the cake with whipped cream using a large open star tip.
5. Garnish with additional crushed cookies.