Preheat the oven to 175°C. Grease an 8x8-inch square tin. 

Take a bigger square of parchment or baking paper and tuck it in, making it stick to the base and sides.

Take 100 gm cream cheese, 3 tbsp icing sugar, 1/2 tbsp vanilla extract and zest of half an orange (optional). Mix using an electric beater or whisk. Keep aside.

In a bowl mix 1 egg, 75 ml water and 75 gm melted butter. Empty the contents of the brownie mix into the bowl and mix quickly using a whisk or a wooden spoon. Mix well till smooth.
Pour the batter and spread it in the lined cake tin. Using a spoon drop small amounts of the cream cheese mixture on the batter about 1 inch apart. Run a knife or toothpick through it in a cutting action to create a marble effect.