Preheat your oven to 350°F (175°C). Line an 8x8-inch square metal baking pan with parchment paper, leaving an overhang on the sides for easy lifting. Lightly grease with baking spray.

In a medium mixing bowl, beat the softened cream cheese and 1/4 cup sugar with a hand mixer on medium speed for 1 minute until completely smooth and lump-free. Add the pumpkin puree, egg yolk, pumpkin pie spice, and vanilla. Beat on low speed just until combined and velvety. Set aside.

In a heatproof bowl set over a pot of simmering water (or in 30-second microwave bursts), melt butter and chopped chocolate together until smooth. Whisk in granulated sugar and dark brown sugar while warm. Whisk in eggs, egg yolk, and vanilla vigorously for 1 minute until batter is glossy. Fold in sifted cocoa powder, flour, and sea salt with a rubber spatula just until combined (do not overmix!).

Spread about 3/4 of the thick brownie batter evenly into the prepared pan. Spoon dollops of the pumpkin cheesecake mixture across the brownie layer. Drop remaining brownie batter in small spoonfuls over the top. Drag the tip of a butter knife or wooden skewer through the batters in figure-eight loops to create a beautiful, marbled swirl pattern.

Bake at 350°F (175°C) for 32 to 36 minutes, until the center is set and edges just pull away slightly from parchment. A toothpick inserted into the brownie portion should come out with a few moist crumbs, not wet batter. Cool completely in the pan on a wire rack for 2 hours, then chill in the refrigerator for 1 hour for ultra-clean, sharp bakery squares!