Adapted from Ready For Dessert, David Lebovitz 2010
6 tablespoons unsalted butter, cut into pieces
4 ounces bittersweet or semisweet chocolate, chopped
2/3 cup sugar
2 large eggs, at room temperature
1/2 cup flour
1 tablespoon unsweetened cocoa powder
1/8 teaspoon salt
1 teaspoon vanilla extract
1/2 cup chocolate chips
8 ounces cream cheese, at room temperature
1 large egg yolk
5 tablespoons sugar
1/8 teaspoon vanilla extract
Line a 9-inch square pan with foil, making sure it goes up all four sides. Use two sheets if necessary. Butter foil lightly, set aside.
Preheat oven to 350 degrees
In a medium saucepan, melt the butter and chocolate over low heat, stirring until smooth.
Remove from heat and whisk in the 2/3 cup sugar, then the eggs.
Stir in the flour, cocoa powder and salt, then the vanilla and chocolate chips until fully incorporated.
Pour into prepared pan and spread evenly with a spatula.
In the bowl of an electric mixer (hand-held or paddle) beat together the cream cheese, the yolk, 5 tablespoons of sugar, and vanilla until smooth.
Scatter eight dollops of the cream cheese mixture on top of the brownie mixture.
Using a dull knife or spatula swirl the cream cheese mixture with the chocolate batter. The batter will look marblized.
Bake for 35 to 40 minutes, or until the batter in the center of the pan feels just set.
Place pan on a rack and Let cool completely, then lift out the foil and peel it away. Cut the brownies into small squares.