• Preheat the oven to 325 degrees F.
• Line a 9×13-inch pan with nonstick foil.

Brownie batter:

• In a medium sized microwave-safe bowl melt the butter, then add the sugar and stir to combine. Return the mixture to the microwave briefly, just until it’s hot but not bubbling.
• Stir in the cocoa, salt, baking powder and vanilla.
• Whisk in the eggs.
• Add the flour and chips.
• Stir smooth.

Cheesecake batter:

• Beat the cream cheese until smooth.
• Add the sugar and vanilla, blending until smooth.
• Add the mascarpone cheese.
• Add eggs until smooth.
• Spread three-quarters of the brownie batter into the prepared pan.
• Spoon the cheesecake batter over the brownie batter, smoothing it out.
• Drop spoonfuls of the reserved brownie mix on top.
• Use a knife to swirl through the cheese and brownie making it marbled.
• Bake for 40-45 minutes.
• Cool, chill and cut!
• Serve with hot fudge if desired.