1. Preheat oven to 350 degrees and spray a 9x13 baking dish with pam baking spray
2. Start with making the brownie layer first
3. Using a medium bowl, whisk the flour, cocoa powder and salt until combined
4. Using a microwave safe bowl, melt the butter and 3 C semi sweet chocolate chips on 45 second increments, just until melted.
5. Stir until smooth
6. Allow the chocolate mixture to cool for about 5 minutes
7. Whisk in the sugar until combined
8. One by one, whisk in the eggs until combined
9. Whisk in the vanilla extract
10. Gradually mix in the dry ingredients until combined and smooth
11. Fold in the last cup of chocolate chips
12. Spread the brownie batter into the baking dish evenly
13. Place 24 oreo cookies into an even row on top of the brownie batter
14. Set aside while you make the rainbow layer

Chocolate Chip Rainbow Cookie Layer

1. Using a standing mixer with a paddle attachment, beat the butter, sugar and light brown sugar until light and fluffy
2. Beat in the eggs, vanilla, salt and baking soda until combined
3. Gradually beat in the flour until a soft dough forms
4. Gently fold in the chocolate chips
5. Evenly divide the chocolate chip batter up between the four bowls
6. Mix in a few drops of red into one of the bowls. Repeat with each of the other colors in separate bowls.
7. Starting with the red cookie dough first, scoop out about 3 tbsp of dough
8. Press the red dough gently on top of the Oreos and into a even thin line
9. Repeat the steps with the orange, yellow and green cookie doughs. You want these four colors to be in even straight rows of color.
10. Once you have your colored dough in straight rows, place the baking dish into the preheat oven and bake for 30-35 minutes or until a toothpick comes out clean
11. Allow to cool before cutting into bars.