Hi carolinagail,
No cornmeal is not necessary for deep dish and i am not aware of any deep dish places in Chicago using it. There are many recipes here that omit corn meal. do you have a scale? chiguy
Ingrediants needed, All purpose Flour, Yeast, Corn Oil, Salt(i feel a must),Mozzarella Cheese, Tomatoes Crushed in Puree or Whole peeled can also work. Parmesan Cheese sprinkled before or after baking.