1. Preheat the Oven:

• Set oven to 350°F (175°C).

• Grease a 9-inch springform pan thoroughly.

2. Prepare the Brownie Layer:

• Mix brownie batter as directed on the box.

• Pour batter into the greased springform pan.

• Bake for 20–25 minutes, or until the center is just set.

• Let cool slightly while you prepare the cheesecake filling.

3. Make the Cheesecake Layer:

1. In a large bowl, beat softened cream cheese until creamy.

2. Add sugar and vanilla extract. Mix until smooth.

3. Beat in the eggs one at a time, scraping the sides between additions.

4. Fold in sour cream and mix until fully combined.

5. Pour cheesecake batter over the slightly cooled brownie layer.

4. Bake the Cheesecake:

• Reduce oven temperature to 325°F (160°C).

• Place the springform pan on a baking sheet and bake for 50–55 minutes, until the edges are set and the center is slightly jiggly.

• Turn off the oven, crack the door open, and let the cheesecake sit for 1 hour.

• Remove and cool completely, then refrigerate for at least 4 hours or overnight.

5. Make the Hot Fudge Sauce:

• In a small saucepan over low heat, combine chocolate chips, heavy cream, butter, and salt.

• Stir constantly until the mixture is melted, smooth, and glossy.

• Let cool slightly before using.

6. Assemble the Cheesecake:

1. Remove chilled cheesecake from the pan and place on a serving platter.

2. Pour the warm hot fudge sauce generously over the top.

3. Garnish with whipped cream, maraschino cherries, and chopped nuts if desired.

7. Serve:

• Slice and serve chilled for the best texture and flavor.

• Optional: Add a scoop of ice cream for the ultimate sundae experience.