Make the Brownie Batter

• Preheat the oven to 350°F. Line an 8×8-inch baking pan with parchment paper, leaving overhang on two sides.
• In a microwave-safe bowl, combine the butter and ½ cup of the chocolate chips. Microwave in 20-second intervals, stirring between each, until melted and smooth. Let cool for 5 minutes.
• In a large mixing bowl, whisk together the granulated sugar, brown sugar, and eggs for 1–2 minutes, until slightly thickened.
• Add the melted chocolate mixture and vanilla extract. Whisk until smooth.
• Add the flour, cocoa powder, and salt. Fold gently until just combined.
• Fold in the remaining ½ cup chocolate chips.

Make the Pumpkin Cheesecake Swirl

• In a separate bowl, beat the softened cream cheese and sugar until smooth and creamy.
• Add the pumpkin purée, egg yolk, vanilla extract, and pumpkin pie spice. Mix until fully combined.

Assemble

• Spread approximately ¾ of the brownie batter evenly into the prepared pan.
• Spoon the pumpkin cheesecake mixture over the brownie batter, spreading gently into an even layer.
• Drop small spoonfuls of the remaining brownie batter over the cheesecake layer.
• Use a butter knife to gently swirl the brownie batter through the cheesecake. Don't overmix! You want distinct ribbons of chocolate and pumpkin cheesecake.

Bake

• Bake for approximately 30–38 minutes, or until the edges are set and the center no longer looks wet or liquid. The cheesecake may have a slight jiggle but should not ripple when the pan is moved.
• Remove from the oven and cool completely in the pan on a wire rack.
• For cleaner slices, refrigerate for 30–45 minutes once cooled. The brownies will become firmer as they cool.

Make the Hot Fudge Sauce

• Add the chocolate chips, milk, butter, corn syrup, cocoa powder, and salt to a small saucepan.
• Heat over medium-low heat, stirring continuously, until the chocolate melts and the mixture becomes smooth and glossy. Do not boil vigorously.
• Remove from the heat and stir in the vanilla extract.
• Let the sauce cool for 5–10 minutes, stirring occasionally. It should thicken into a rich, pourable fudge sauce.

Assemble

• Lift the cooled brownies from the pan and cut into 9 large squares.
• Place one brownie on a plate and generously drizzle with warm hot fudge sauce.
• Serve immediately while the fudge is glossy and drippy.