Preheat oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.
In a large bowl, whisk together melted butter and sugar. Add cocoa powder and vanilla extract, mix until well combined.
Beat in the eggs one at a time. Stir in the flour and salt until just combined. Do not overmix.
In a separate bowl, beat cream cheese and sugar until smooth. Beat in the egg and vanilla extract.
Pour half of the brownie batter into the prepared pan. Dollop spoonfuls of the cream cheese mixture over the brownie batter. Swirl gently with a knife.
Pour the remaining brownie batter over the cream cheese layer. Swirl again gently.
Bake for 30-35 minutes, or until a toothpick inserted near the center comes out with moist crumbs attached.
Let cool completely before cutting into squares.
Notes
For an extra rich flavor, use good quality cocoa powder. Ensure cream cheese is at room temperature for a smooth swirl.