Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking pan.
In a large saucepan, melt the butter over medium heat.
Add sugar to the melted butter and stir until well combined.
Remove from heat and allow to cool slightly.
Stir in the eggs one at a time, mixing well after each addition.
Add vanilla extract and mix until incorporated.
Sift together flour, cocoa powder, and salt in a separate bowl.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in the chopped Oreo cookies gently into the batter.
Pour the batter into the prepared baking pan and smooth the top. Add extra Oreos on top.
Bake for 30 minutes or until a toothpick inserted comes out with a few moist crumbs.