- Preheated the oven to 160°C fan/180°C. 
- In a bowl over a pan of simmering water, melt together the butter and dark chocolate. 
- Once melted, remove from the heat and sieve in the cocoa powder and plain flour. 
- In a seperate bowl, with an electric whisk, whisk together the eggs and caster sugar for 7-8 minutes until it double in size and becomes light and pale. 
- Pour a little bit of the melted chocolate and butter into the egg mixture and fold through. Repeat this until all of the chocolate mixture is fold through the egg mixture. 
- Add in the white chocolate chunks and broken golden oreo pieces. You may want to leave a few biscuits left to place on top of the brownies. 
- Pour the mixture into a 8" inch lined square tin and bake in the preheated oven for 25 minutes 
- Once cooked, allow the brownies to cool in the tin fully before sliceing in to 9 squares.