HEAT oven to 325°F. Coat 13 x 9-inch baking pan with no-stick cooking spray. Prepare brownie mix according to package directions using the oil, water and 2 eggs. Spread evenly in prepared pan.
BEAT cream cheese, butter, cornstarch and 1/4 teaspoon cinnamon in medium bowl with electric mixer on medium speed until fluffy. Add sweetened condensed milk, 1 egg and vanilla. Beat until smooth. Pour evenly over brownie layer. Sprinkle with remaining 1/2 teaspoon cinnamon.
BAKE 48 to 52 minutes or until top is lightly browned and filling is set in center. Cool completely in pan on wire rack. Place frosting into corner of 1-quart heavy-duty resealable plastic bag. Microwave on HIGH 5 to 10 seconds. Cut small corner off bag. Drizzle over brownies. Chill 30 minutes before serving.