**1. Make and Bake the Brownie Base:**
* Preheat oven to 350°F (175°C). Grease and line a 9-inch springform pan with parchment paper.
* In a medium bowl, whisk together the melted butter, sugar, and cocoa powder.
* Whisk in the eggs one at a time, followed by the vanilla.
* Stir in the flour and salt until just combined.
* Pour the batter into the prepared pan and spread evenly. Bake for 15-20 minutes. The brownie should be mostly set but still slightly soft. Let it cool slightly.
**2. Make and Bake the Cheesecake Filling:**
* Reduce oven temperature to 325°F (160°C).
* In a large bowl, beat the softened cream cheese and sugar with an electric mixer until smooth and creamy.
* Beat in the sour cream and vanilla extract.
* Add the eggs one at a time, mixing on low speed until just combined. Do not overmix.
* Pour the cheesecake filling over the par-baked brownie base.
* Place the springform pan in a large roasting pan and fill the roasting pan with hot water to about halfway up the side of the springform pan (a water bath).
* Bake for 60-75 minutes, or until the edges are set and the center has a slight jiggle. Turn off the oven and let the cheesecake cool in the oven with the door propped open for 1 hour.
* Remove from the oven and water bath. Let it cool completely on a wire rack, then refrigerate for at least 6 hours, or preferably overnight.
**3. Make the Caramel Topping:**
* In a medium saucepan, melt the sugar over medium heat, stirring constantly until it dissolves and turns a light amber color.
* Remove from heat and carefully whisk in the butter until melted. The mixture will bubble up.
* Slowly pour in the heavy cream while whisking constantly until the sauce is smooth.
* Let the caramel cool to a thick, pourable consistency.
**4. Decorate and Serve:**
* Carefully remove the chilled cheesecake from the springform pan.
* Pour the caramel topping evenly over the cheesecake, allowing it to drip down the sides.
* Garnish the top with the large chocolate chunks.
* Slice with a warm knife and serve.
