Preheat the oven to 350 degrees and line a small 8x8 baking pan with parchment paper.
Melt the butter and semisweet chocolate together in a microwave-safe bowl, stirring until smooth. Stir in 3/4 cup sugar, then add the two eggs one at a time and mix well.
Add the flour, cocoa powder, and salt to the chocolate mixture and stir until just combined. Pour most of the batter into the prepared pan and spread evenly.
In a separate bowl, beat the cream cheese until smooth. Mix in the pumpkin puree, 2 tablespoons sugar, egg yolk, and cinnamon until fully blended.
Drop spoonfuls of the pumpkin mixture over the brownie batter. Use a knife to gently swirl the two together, leaving some distinct areas of each. Spread any remaining brownie batter lightly on top if desired.
Bake for 25 to 28 minutes until the center is set but still slightly soft. Cool completely in the pan before cutting.