From wikipedia:
In addition to Chicago-style deep-dish pizza, there is also a thin-crust pizza unique to Chicago, sometimes referred to as "flat" pizza.
[5] The crust is thin and firm enough to have a noticeable crunch, unlike a
New York-style pizza, yet thick enough to be soft and doughy on the top.
The crust is topped with a liberal quantity of
Italian style tomato sauce, which is usually quite herbal or highly spiced, and typically contains no visible chunks of tomato. Next, a layer of toppings is added, and finally a layer of mozzarella cheese.
Traditionally, this pizza is cut into squares, also known as "party cut," as opposed to a "pie cut" into wedges. The consistency of the crust and the quality and quantity of the tomato sauce and cheese are what separate this style from East Coast-, Roman- and
St. Louis-style pizzas, and it makes the pizza from neighborhood pizzerias immediately distinguishable from that offered by national chains such as
Papa John's or
Pizza Hut.
This style of pizza is now spreading due to the expansion of Aurelio's Pizza, a Chicago chain, into
Florida,
Colorado and a few other states. Additionally, Sweet Home Chicago Pizzeria now sells the authentic Chicago-style thin-crust pizza in the
Salt Lake City,
Utah, market, as well as
Rush Street Neighborhood Grill in
Kingsport, Tennessee.
Hearty, coarse
Italian sausage is the number-one pizza topping in Chicago.[
citation needed] Some restaurants lay on the sausage so thickly that it covers the whole surface of the pizza, like a giant sausage disk. Other common pizza toppings in Chicago include pepperoni, spinach, onion, green peppers, black olives, and mushrooms.
It is uncommon to see any sort of
California-style pizza toppings on a Chicago-style pizza.