Prepare brownie mix as directed on package; spread in greased 13x9 inch baking pan. Beat cream cheese with electric mixer on medium until smooth. Add sugar, egg and vanilla and mix ONLY until blended. Pour cream cheese mixture over brownie mixture. Cut through several times with knife for marble effect. Bake at 350 degrees for 35-40 minutes or until cream cheese mixture is lightly browned. Cool and cut into squares.