Remove the pans from the oven, place the oven rack in the middle position, and start preheating the oven to 550°F (290°C). If your oven cannot get that hot, then set it to 450°F (232°C) and adjust the time in by adding 2 to 3 minutes. While the oven is preheating, let's prep the pizzas.
At this point, the dough should be mostly filling the pan up to the edges. Use your fingertips to press it around until it fills in every corner. If you see any large bubbles of air, pop them as you work the dough, and then lift up the edges of the dough to let any air bubbles underneath from escape. The dough should be be lumpy but evenly spread over the cast iron pan.
Top each round of dough with 3/4 cup of your favorite pizza sauce (or check out my recipe for a homemade sauce). Spread the sauce to the very edge with the back of a spoon, and then sprinkle the mozzarella cheese evenly all the way to the edge. Season with salt. This is where you add your favorite toppings.
Transfer each cast iron pan to oven and bake until the top is golden brown and bubbly and the bottom is golden brown and crisp, between 12 to 15 minutes. To check the bottom, lift it with a thin spatula to peek underneath. If the bottom is not as crisp as desired, place the pan over a burner and cook on medium heat, moving the pan around to cook evenly until it is crisp, 1 to 3 minutes.
Remove the pizzas and transfer to a cutting board and sprinkle with grated Parmesan or Pecorino Romano cheese. Cut each pizza into 6 slices and serve immediately.