Preheat oven to 350 degrees. Spray a 9 x 13 baking dish with non-stick cooking spray.
In a large mixing bowl, using an electric hand mixer, beat together butter, eggs, brown sugar, granulated sugar, salt, and vanilla until smooth.NOTE: butter should be very soft. heat in microwave for 10-15 seconds at a time until very soft.
Add in flour and banana. Beat again until combined.
Fold in 2 cups of chocolate chips. NOTE: Batter will be thick.
Place batter into prepared baking dish and smooth evenly. Sprinkle remaining chocolate chips on top of batter evenly.
Bake in preheated oven for 35-40 minutes until toothpick comes out clean inserted into center of brownie.
Remove and allow to cool completely before serving.
