HEAT oven to 350°F. Spray bottom only of 9-inch springform pan with no-stick cooking spray. Prepare brownie according to package directions for chewy brownies. Reserve 3/4 cup brownie batter for cheesecake. Spread rest evenly in prepared pan.
BAKE 25-30 minutes or until set
BEAT cream cheese until fluffy in large bowl. Gradually beat in sweetened condensed milk. Add eggs and vanilla; mix well. Stir in chocolate chips. Pour into prepared pan. Add a lttle less than a 1/4 cup water to reserved brownie batter and mix well. Drop spoonfuls of brownie batter randomly over cream cheese mixture. Swirl with tip of knife to create marbled effect.
REDUCE oven temperature to 300°F. Bake 50 minutes or until set. Cool. Chill thoroughly. Remove side of springform pan. Garnish as desired.
NOTE: Chocolate chips may fall to the bottom of brownie layer during baking.