Preheat the oven to 180 degrees Celsius (350 degrees F)
Melt the butter
Pour the melted butter into the mixer and add the caster sugar and vanilla extract.
Mix together well.
Break the eggs into a small bowl and beat them together. Add the beaten eggs to the butter and sugar mix a little at a time and mix well.
Sift the flour, cocoa powder and baking powder together
Add the dry ingredients to the wet ingredients a spoon at a time with the mixer on low until thoroughly combined.
Chop the Oreo biscuits into small pieces and add to the brownie mix and stir until combined. Don't stir too much or the biscuits will break up, you want fairly large chunks of cookie in the mixture.
Pour into a greased and lined tray and smooth the surface to make an even layer. Bake for about 30 minutes. They are cooked when they have risen and formed a crust on top. The middle should be soft.
Leave the brownies to cool in the tin for about ten minutes then cut into squares. Leave the brownies on a wire rack to cool completely.
This is how they should look 😊