Preheat the oven to 165℃. Line a 20 cm square baking tin with baking paper.
Melt the butter in a small saucepan over a medium heat.
Once melted, pour the butter into a large mixing bowl and add the granulated sugar and the light muscovado.
Beat it with a whisk for a few minutes until it thickens slightly.
Add the two eggs and vanilla bean paste and mix until well combined.
Now add the plain flour and custard powder, mix well until you have a fudgy brownie like texture.
Fold through the broken Golden Oreos and white chocolate chips.
Place the mixture into the lined baking tin, spread it into the edges evenly and then bake for 28-30 minutes.
Leave it to cool to room temperature, then for best results place it into the fridge to cool for an hour or so.
Cut into portions and serve.
