Preheat oven to 350 degrees. In a large mixing bowl, cream together butter, sugar, and brown sugar for 3-4 minutes or until light and fluffy. Add eggs one at a time, mixing well after each addition. Add vanilla.
Stir in cocoa, flour, baking soda, and salt until mixed together. Fold in chocolate chips. Pour into 9 x 13 pan and spread evenly.
In a large mixing bowl, cream together butter, brown sugar, and sugar for 3-4 minutes. Add egg and vanilla and mix for 1 minute longer.
Stir in flour, baking soda, and salt. Fold in chocolate chips. Drop spoonfuls of cookie dough on top of the brownie batter, evenly, to try to cover most of it.
Bake for 28 to 32 minutes or until the edges begin to set-up. If you are using milk chocolate chunks, sprinkle on the top the last 5 minutes of baking time. Once the bars are baked, let cool before cutting. To make it easier to cut, place the bars in the freezer for 20-30 minutes.