1. Combine butter, chocolate and brown sugar in a medium saucepan and stir over medium heat until chocolate and butter have melted. Remove from heat and whisk in eggs.
2. Add flour, cocoa, and baking powder and stir until well combined. Pour into a greased and lined 18cm x 28cm rectangular tin.
3. Beat Philly and caster sugar until smooth and creamy. Spoon randomly over chocolate mixture and swirl with the tip of a knife. Bake at 180 ºC, 350 ºF, Gas Mark 4 for 35 - 40 minutes or until cooked through. Allow to cool before slicing.
And I can honestly say, this recipe is EASY, looks like you've spent hours slaving over the stove, and taste Ah-may-zing!