Position a rack in the middle of the oven and preheat to 350 degrees F. Line a 9 by 13-inch baking pan with parchment paper, so that the edges of the paper come up the sides. Lightly butter the paper.
Put both the semisweet and unsweetened chocolates and the butter in a heatproof medium bowl. Fill a medium saucepan with a couple inches of water and bring to a simmer over medium heat. Turn off the heat; set the bowl of chocolate over the water to melt. Whisk until smooth. (Alternatively, melt in a microwave at half power, for 1 minute, stir and then heat for another minute or until melted.)
Whisk the flour and salt in a bowl.
In a large bowl whisk together the eggs, sugar, and vanilla. Stir the chocolate mixture into the egg mixture until smooth. Add the dry ingredients and mix until just blended. Take care not to over mix the batter. Transfer the batter to the prepared pan.
For the marble swirl: Whisk the cream cheese with the sugar, egg, and vanilla until smooth. Drop very large spoonfuls of the cream cheese mixture onto the surface of the brownie batter. Insert a butter knife through the batter to the bottom of the pan. With the flat edge of the knife, make swirling motions through the batters, occasionally lifting the knife through the top, until the dark and light batters are marbled.
Bake until a toothpick inserted into the center of the brownies comes out coated with a fudge-y crumb, 30 to 35 minutes. Cool the brownies in the pan on a rack.
To take the brownies out of the pan, lift the edges of the paper. Cut the brownies into squares. Serve.
Copyright 2003 Television Food Network, G.P. All rights reserved
Recipe courtesy of Food Network Kitchens