Cream Cheese Brownies

My MIL introduced me to a delish brownie recipe that always gets requests for the recipe.
Start with a boxed brownie mix (9x13 size). I prefer Betty Crocker, but whatever you have on hand will work fine. Follow the instructions for the cake-like brownies, pour into greased pan and set aside. Use the same bowl and beat 1 pkg. of SOFTENED cream cheese (yes, use the 1/3 less fat stuff, it works great and you'll probably end up eating half the tray, so you should save where you can). Add 1/3 c. sugar and beat until light and fluffy. Add 1 egg and 1/2 tsp. vanilla, mix until fully incorporated. Drop cream cheese mixture by spoonfuls onto the brownie mix. Use a knife back and forth length- and width-wise several times to create a marble effect. Sprinkle with 1 1/2 c. semi-sweet chocolate chips.
Bake about 35 minutes, until the cream cheese is turning golden brown and a toothpick tests done. Allow to cool and cut into squares. I usually try to cut them small so I can justify eating more of them. They will still taste very good for 5 or so days if you keep them covered, but they likely won't last that long.
I have also tried substituting chopped Reeses PB cups or crushed Oreos for the chocolate chips, but the original way is still my favorite.
(I made these for a neighborhood party and got so caught up in the cutting and plating I forgot to take a finished picture, sorry.)