The Chicago Style Deep Dish Pizza was first created at The Pizzeria (later Pizzeria Uno) in 1943 in Chicago, Illinois. It is differentiated from other pizzas by being formed and baked in a deep pie pan instead of the typical flat baking sheet or pizza stone. I used a 9 inch Springform Pan. A deep 9 inch cake or pie pan also works well. The dough usually has semolina or cornmeal added to create a hint of yellow in the crust. The majority of the cheese is added before the filling and tomato sauce to prevent it from burning due to the longer baking time.
More information on the history of the Chicago Style Deep Dish Pizza.
I only used about 3/4ths of the sausage filling for the pizzas. The remainder was perfect for omelets the next morning! You can omit the sausage filling altogether, if desired, or substitute it with a filling of your choice. Instead of using an entire onion, I just used the remaining onion from the 4 tablespoons used for the tomato sauce.