Make the Brownie Batter
2 Preheat the oven to 350°F. Line an 8×8-inch baking pan with parchment paper, leaving overhang on two sides.
3 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.
4 In a large mixing bowl, whisk together the granulated sugar, brown sugar, and eggs for 1–2 minutes, until slightly thickened.
5 Add the melted chocolate mixture and vanilla extract. Whisk until smooth.
6 Add the flour, cocoa powder, and salt. Fold gently until just combined.
7 Fold in the remaining ½ cup chocolate chips.
Make the Pumpkin Cheesecake Swirl
9 In a separate bowl, beat the softened cream cheese and sugar until smooth and creamy.
10 Add the pumpkin purée, egg yolk, vanilla extract, and pumpkin pie spice. Mix until fully combined.
Assemble
12 Spread approximately ¾ of the brownie batter evenly into the prepared pan.
13 Spoon the pumpkin cheesecake mixture over the brownie batter, spreading gently into an even layer.
14 Drop small spoonfuls of the remaining brownie batter over the cheesecake layer.
15 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
17 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.
18 Remove from the oven and cool completely in the pan on a wire rack.
19 For cleaner slices, refrigerate for 30–45 minutes once cooled. The brownies will become firmer as they cool.
Make the Hot Fudge Sauce
21 Add the chocolate chips, milk, butter, corn syrup, cocoa powder, and salt to a small saucepan.
22 Heat over medium-low heat, stirring continuously, until the chocolate melts and the mixture becomes smooth and glossy. Do not boil vigorously.
23 Remove from the heat and stir in the vanilla extract.
24 Let the sauce cool for 5–10 minutes, stirring occasionally. It should thicken into a rich, pourable fudge sauce.
Assemble
26 Lift the cooled brownies from the pan and cut into 9 large squares.
27 Place one brownie on a plate and generously drizzle with warm hot fudge sauce.
28 Serve immediately while the fudge is glossy and drippy.
