In small bowl, stir together pumpkin, spices (cinnamon, ginger, nutmeg), and 1/4 teaspoon salt. Set aside.
In a separate bowl, beat the mascarpone cheese and cream cheese with 1/4 teaspoon salt for 30 seconds. Add pumpkin mixture and mix until just combined.
Add sugar, flour and vanilla, and mix until just combined. Add egg yolks one at a time, and beat until incorporated. Set aside.
Preheat the oven to 325 degrees. Butter the bottom of a 9 x 9-inch baking dish and line with parchment paper. Whisk together flour, cocoa powder, baking powder, and salt in a large bowl.
In separate bowl, stir together the melted butter and sugar. Whisk in eggs and vanilla until incorporated. Stir in chocolate chips, then slowly add flour mixture to egg mixture. Mix until just combined.
Reserve 1/2 cup brownie batter. Spread remaining brownie batter evenly into prepared pan. Pour cheesecake mixture over brownie batter. Use a spoon to make 3 to 4 lines with reserved brownie batter on top of cheesecake layer. Use a toothpick or small knife to swirl brownie batter lines into cheesecake layer.
Bake for 45 minutes or until top of brownies is just set and tester comes out mostly clean. Cool completely and refrigerate to chill before serving.