2/3 Cup all-purpose flour
1/4 Teaspoon salt
1/2 Teaspoon baking powder
2 Ounces unsweetened chocolate
4 Ounces bittersweet or semisweet chocolate
1 Stick butter
1 Cup sugar
2 Teaspoons vanilla
3 Large eggs
Cream Cheese Mixture
1/4 Cup Sugar
1/2 Teaspoon vanilla
1 Large egg yolk
8 Ounces cream cheese, room temperature
Adjust oven rack to lower-middle position, and preheat oven to 325 degrees.
Whisk flour, salt, and baking powder in a small bowl, set aside.
Line an 8-inch-square baking pan with a sheet of aluminum foil in the bottom of pan. The foil overhangs both sides of the pan; use as handles to removed baked brownies from pan. Coat foil with cooking spray.
In a medium heat-proof bowl set over a pan of almost simmering water, melt chocolate and butter, stirring occasionally until mixture is smooth. (Alternatively, melt chocolate and butter in microwave oven. Microwave chocolate alone at 50% power for 2 minutes. Stir chocolate; add butter; and continue microwaving at 50% for another 2 minutes, stopping to stir the mixture after 1 minute. If chocolate is not entirely melted, microwave an additional 30 seconds at 50% power.)
Remove melted chocolate mixture from heat; whisk in sugar and vanilla.
Whisk in eggs, one at a time, fully incorporating each before adding the next.
Continue whisking until mixture is completely smooth.
Add dry ingredients; whisk until just incorporated.
In a small bowl, beat cream cheese with sugar, vanilla and egg yolk until even consistency.
Pour 1/2 the brownie batter into prepared pan.
Drop 1/2 the cream cheese mixture, by spoonfuls, over batter. Repeat layering with remaining brownie batter and cream cheese filling. Use blade of table knife or spoon handle to gently swirl batter and cream cheese filling, creating a marbled effect
Bake until edges of brownies have puffed slightly, center feels not quite firm when touched, and a toothpick inserted into center comes out with several moist, fudgy crumbs. 50 minutes.
Cool for 5 minutes. Using foil handles, lift brownies out of the pan, allow to cool to room temperature. Refrigerate until chilled, at least 3 hours. Cut into squares.