Heat oven to 350°F. Line a 13 x 9 x 2-inch baking pan with aluminum foil. Coat with nonstick cooking spray.
In medium-size bowl, whisk together flour, baking powder and salt until blended.
In large microwave-safe bowl, combine butter and chocolate. Microwave on high for 1 minute; stir until smooth. If necessary, microwave another 15 seconds to melt.
Add sugar to chocolate mixture; stir to combine. Add eggs and vanilla; stir until smooth. Stir in flour mixture until smooth. Spoon into prepared pan; spread evenly.
In medium-size bowl, on medium speed, beat cream cheese until smooth. On low speed, beat in flour, sugar and vanilla until blended. Add milk; beat until smooth.
With a tablespoon, make a depression or dimple in top of brownie batter. With another tablespoon, drop a dollop of cream cheese mixture into the dimple. Continue to make and fill dimples over the top in an uneven pattern until there are lots of them. (Don'tworry about being too neat since mounds will flatten out during the baking.)
Bake in 350°F oven 30 minutes or until firm to touch and set. Let cool in pan on wire rack for 15 minutes. Using foil, remove brownie from pan to rack. Let cool about 2 hours before cutting. Store airtight for up to 1 week.