Preheat oven to 350 degrees Fahrenheit.
Line a 9"x13" baking pan with parchment paper so it hangs over the sides slightly.
In the bowl of an electric mixer, cream together softened butter, brown sugar, eggs and vanilla.
In a separate bowl, whisk together flour, baking cocoa, baking soda and salt.
Add the flour mixture to the wet mixture and mix just until incorporated.
Press dough into the parchment-lined baking pan. Press 20 whole Rolos evenly into the top of the dough. Sprinkle with the 15 chopped Rolos and press those slightly into the top of the dough.
Bake for approximately 12-14 minutes, or just until set. Be careful not to over bake!