Preheat the oven to 350 degrees Fahrenheit.
In a large mixing bowl, cream together softened butter, sugar, and brown sugar for 3-4 minutes or until the mixture is light and fluffy. Add eggs one at a time, mixing well after each addition. Then, add vanilla.
Stir in all-purpose flour, cake flour, cocoa, and salt until well combined.
Gently fold in the chocolate chips.
Pour the batter into a 9 x 13-inch pan, spreading it evenly.
Bake for 28-36 minutes.