Preheat oven to 165C° (330F°).
Line a slice tin with baking paper.
In a microwave safe bowl, add dark chocolate, butter, and 1 Terrys Orange ball. Microwave on 30 second bursts, stirring each time until melted. Set aside to cool.
Use you mixer to whisk the eggs and sugar until pale and doubled in size.
Roughly chop the remaining 2 Terrys Orange balls and set aside
Poor the cooled chocolate mix into the egg mixture and fold together gently. This will take some time but don't rush it or go to hard you don't want to knock out all the air.
Gently fold through the chopped Terrys chocolate.
Pour into the prepared slice tin and bake for 30-40 minutes. If the brownie starts to burn around the edges cover it with foil. It will be done when it just wobbles slightly in the centre. Allow to completely cool in the pan before slicing.
