1. Make and Bake the Brownie Base:

• Preheat the oven to 350°F (175°C). Line the bottom of a 9-inch springform pan with parchment paper. Grease the parchment and the sides of the pan.
• In a medium-sized bowl, combine the brownie mix, melted butter, eggs, and 2 tablespoons water. Stir until the batter is well combined and no dry streaks remain.
• Pour the batter into the prepared springform pan and spread evenly.
• Bake for 20-24 minutes, or until a toothpick inserted into the center comes out clean or with fudgy crumbs (follow mix instructions, adjusting slightly for the pan size if needed).
• Allow the brownie to cool completely in the pan on a wire rack.

2. Prepare Mousse Components:

• Bloom Gelatin (Batch 1): In a small dish, sprinkle 1 teaspoon of gelatin over 1 tablespoon of cold water. Let it sit for 5-10 minutes until it solidifies or “blooms.”
• Melt Chocolate: In a microwave-safe bowl, combine the mini chocolate chips and 1 tablespoon of heavy whipping cream. Microwave in 30-second increments, stirring in between, until the chocolate is melted and smooth.
• Add Gelatin to Chocolate: Microwave the bloomed gelatin (Batch 1) for 8-10 seconds until it turns back into a liquid. Immediately pour the liquid gelatin into the melted chocolate mixture and stir well to combine. Set aside to cool slightly.
• Chill Mixing Bowl: Place a medium-sized metal mixing bowl in the freezer for 5-10 minutes to chill.
• Bloom Gelatin (Batch 2): Prepare a second batch of gelatin exactly like the first: sprinkle 1 teaspoon gelatin over 1 tablespoon cold water and let bloom.
• Whip Cream: Pour 1 cup of cold heavy whipping cream into the chilled bowl. Beat with an electric mixer on medium-high speed until it starts to thicken.
• Add Gelatin & Sugar to Cream: Microwave the bloomed gelatin (Batch 2) for 8-10 seconds until liquid. With the mixer on low speed, slowly pour the liquid gelatin into the thickening cream. Increase speed to high, add the 3 tablespoons powdered sugar, and continue beating until stiff peaks form. Set this stabilized whipped cream aside.

3. Make the Chocolate Mousse Base:

• In a large bowl (you can use the mixer bowl), beat the softened cream cheese on medium-high speed for 2-3 minutes until completely smooth, scraping the bowl occasionally.
• Add the granulated sugar and beat until well combined.
• Add the cocoa powder and beat until well combined, scraping down the bowl occasionally.
• Slowly add the remaining 2 tablespoons of heavy whipping cream and the teaspoon of vanilla extract; continue beating until combined and smooth.
• Add the slightly cooled melted chocolate-gelatin mixture and mix thoroughly until fully incorporated.

4. Finish the Mousse:

• Gently fold the prepared stabilized whipped cream (from step 2) into the chocolate cream cheese mixture using a rubber spatula. Stir gently from bottom to top until the mixture is well combined and no streaks remain. Be careful not to deflate the whipped cream too much.

5. Assemble the Cake:

• Ensure the brownie base is completely cool in the springform pan. Lining the sides of the pan with parchment paper or an acetate cake collar at this stage can help create cleaner sides.
• Pour the chocolate mousse filling over the cooled brownie base. Spread it evenly with an offset spatula or the back of a spoon.

6. Chill Thoroughly:

• Refrigerate the cake for at least 4 hours, or preferably overnight, until the mousse is completely set and firm.

7. Make Topping and Decorate:

• Prior to serving, prepare the whipped cream topping. Place another medium-sized metal mixing bowl in the freezer for 5-10 minutes to chill.
• Pour the remaining ¾ cup cold heavy whipping cream into the chilled bowl. Beat on medium-high speed until it starts to thicken.
• Add the 3 tablespoons powdered sugar and continue beating on high speed until stiff peaks form.
• Optional Piping: Transfer the whipped cream to a piping bag fitted with a large open star tip and pipe a decorative border around the top edge of the chilled mousse cake. (Alternatively, just spread the whipped cream on top).
• Drizzle the top of the cake (or the whipped cream border) with hot fudge sauce.
• Sprinkle with the additional mini chocolate chips.

8. Serve:

• Carefully run a thin knife around the edge of the cheesecake to loosen it from the springform pan sides (if you didn’t use a collar). Release and remove the pan sides.
• Slice and serve chilled.