Preheat oven to 325°. Lightly butter a 9″x 13″ baking pan. Line with parchment paper or aluminum foil.
Melt chocolate and butter in a double boiler or in the microwave. Set aside to cool.
Whisk together flour, baking powder, and salt. Set aside.
In a large bowl, whisk eggs, egg yolks, sugar, and vanilla. Pour chocolate mixture into egg mixture, whisking to combine. Add flour mixture and stir just until combined.
Pour batter into prepared pan. Spread evenly.
Using an electric mixer, beat cream cheese, sugar, and salt until light and fluffy (about 5 minutes). Add eggs, 2 at a time, mixing well after each addition. Stir in vanilla.
Pour cheesecake mixture over brownie layer. Sprinkle evenly with chocolate chips.
Bake for 1 hour & 15 minutes, or until lightly golden. Cool completely on wire rack before cutting into bars. Store brownies in refrigerator. Serve cold or at room temperature.