Take a heavy bottom pan or a steel bowl. Add chocolate chips in it and melt it using direct method or double boiler method.
Once the chocolate is melted. Add in sugar, vanilla, buttermilk and mix well.
Now add in flour, cocoa, baking soda and mix well.
Add in the water and give it a good mix.
Grease a 15 x 15 cm pan with butter or oil and dust it generously with flour.
Pour the batter into a prepared pan and bake it for 40 to 45 mins. Insert a toothpick in the centre and check whether the tooth pick comes out clean. If it does, then the brownies are baked.
Now sprinkle the top of the brownies with chocolate chips and put it back into the oven for a couple of mins.
Now the chocolate must be melted. Spread the chocolate evenly over the top of the brownies using a spatula or butter knife.
Now crush some Oreo and sprinkle them on top of the brownies.