HEAT oven to 350 degrees F. Spray bottom only of 9-inch springform pan with no-stick cooking spray. Prepare brownie according to package directions for chewy brownies. Spread evenly in prepared pan.
BAKE 35 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.
REDUCE oven temperature to 300 degrees F. Bake 50 minutes or until set. Cool. Chill thoroughly. Remove side of springform pan. Garnish as desired.