Preheat the oven to 350°F and line a 9x9 pan with parchment.
Melt the chocolate and butter together until smooth. Whisk in the sugar, then the eggs and vanilla. Fold in the flour and salt just until combined.
For the swirl, beat the cream cheese, pumpkin, sugar, egg yolk, pumpkin pie spice, and vanilla until smooth.
Swirl and Bake
Spread most of the brownie batter in the pan. Dollop the pumpkin mixture and remaining brownie batter on top, then drag a knife through in an S pattern to marble.
Bake for 40 to 45 minutes, until the center is just set and a toothpick comes out with a few moist crumbs.
Cool completely, then chill for at least 1 hour before cutting into squares.
Notes
Swirl gently: Dollop and drag once, don't overmix or the marble blurs.
Keep fudgy: Use just ¾ cup flour and don't overbake.
Chill to slice: Cold brownies cut into clean squares.