In a saucepan on low heat, melt together the butter and sugar. Then transfer the mixture into a mixing bowl, and set aside to cool.
In a separate bowl, sift together flour, cocoa powder and salt.
Once the sugar mix has cooled slightly, add the eggs and vanilla. Mix well.
Combine the wet ingredients with the dry. Mix well.
Add chocolate chips. Set aside.
The Cream Cheese Swirl
Beat together cream cheese, sugar, vanilla and egg yolk, until well combined.
Once you have the brownie mix all ready, add half of the batter to a lightly greased & dusted dish (see Tips! for dish dusting).
Then add half of the cream cheese mix in clumps over your brownie.
Using a knife, swirl the cream cheese mix, until you have a marbling effect like above.
Then add the remaining brownie batter.
Then add the remaining cream cheese batter in clumps, and swirl again.
Bake in a 325 degree preheated oven for approximately 1 hour. The square will be done when the edges of the brownie have puffed, the centre of the cake feels firm to the touch, and a toothpick when inserted comes out clean. Just check it for doneness, as you may need to bake it longer...
When the cake is done, remove from the oven and let cool to room temperature.
Chill in the fridge for at least 2-3 hours.
Use cocoa powder instead of flour to dust your pan! That way, you won't see the flour on your brownies!