Preheat oven to 350ºF (180ºC). Prepare the brownie mix as the package directs. Grease a 13 x 9-inch glass baking dish with vegetable spray. Evenly spread the brownie mix in the pan.
In the large bowl of a stand mixer beat together the cream cheese, butter and cornstarch until fluffy, about 4 minutes.
Gradually beat in the sweetened condensed milk until completely combined then beat in the egg and vanilla until smooth.
Stir in the raspberries then pour the mixture evenly over the brownie batter. Use a fork to gently swirl the mixture in the pan to create a marbling effect.
Bake until the top is lightly browned, about 45 minutes. Let cool completely then cut into squares.