1Preheat oven to 350 degrees.
Spray a 9x13 baking pan lightly w/cooking spray.
2Prepare the brownie mix as directed on the package.
Adding the walnuts [optional].
Pour into the baking pan. [do not bake yet]
3In a medium bowl, cream the softened cream cheese and sugar until well blended.
Add the egg, flour, baking powder and vanilla; mix until smooth.
4Pour the cream cheese mixture over the brownie mix; cut through with a knife For a marbled effect.
5Sprinkle top with the chocolate chips.
6Bake for 35-45 minutes until lightly browned.
7Cool; cut into squares.
[After cooling, for a neater presentable cut bar; I trim about 1/2 inch all around the pan. Remove it and use it to snack on OR can be crumbled on top of ice cream [either way kids love this]