Brownie mix as directed on package for fudge brownies. Spread batter evenly into 2 greased half-sheet, 12 x 17 inch, pans (or 1 half sheet pan for trial recipe).
Cream cheese, sugar and vanilla in bowl with electric mixer fitted with paddle attachment. Beat on medium speed until well blended. Add eggs, 2 at a time, mixing just until blended after each addition. Pour over batter in pan(s); cut through batter with knife several times for marble effect. Sprinkle with chocolate chips.
In 350°F convection oven for 30 to 35 minutes or until cream cheese mixture is lightly browned. Cool in pan on wire rack. Cut into squares.