Preheat oven to 160’C and place the rack in the center of the oven.
Line a 9 inch (23 cm) square baking pan with aluminium foil.
Melt the butter and chocolate In a heatproof bowl, placed over a saucepan of simmering water.
Remove from heat and whisk in the sugar and vanilla extract.
Add the eggs, one at a time, beating well after each addition.
Stir in the flour and salt and stir vigorously until the batter is smooth and glossy.
Remove 120ml of the brownie batter and set it aside. Spread the remainder of the brownie batter evenly onto the bottom of the prepared pan.
In another bowl whisk together the cream cheese, sugar, vanilla and egg until smooth.
Spread the cream cheese filling evenly over the brownie layer and drizzle over the brownie that was set aside.
Using a knife, swirl the brownie and cheesecake mix together so that it creates a marble effect
Bake in the preheated oven for about 35-40 minutes, or until the brownies are set and the cream cheese is just beginning to brown. If you are unsure stick a cocktail stick into the middle of the brownie, if if comes out with just a few crumbs attached then it is done.
Remove from oven and place on a wire rack to cool completely, cover and refrigerate the brownies until they are firm enough to cut into squares. This could take several hours.
Once chilled, cut into squares or rectangles with a sharp knife.