In a small bowl, combine warm water, sugar, and active dry yeast. Stir gently and let sit for 5-10 minutes until foamy.
In a large mixing bowl, whisk together flour, cornmeal, and salt.
Add the melted butter and the yeast mixture to the dry ingredients. Mix until a dough forms.
Turn the dough onto a lightly floured surface and knead for about 7-8 minutes until smooth and elastic.
Place the dough in a lightly oiled bowl, cover with a clean kitchen towel, and let it rise in a warm place for 1 hour or until doubled in size.
While the dough rises, prepare the sauce: In a medium saucepan, heat 1 tablespoon olive oil over medium heat.
Add the chopped onion and cook for 5 minutes until softened.
Add the minced garlic and cook for 1 minute until fragrant.
Stir in the crushed tomatoes, oregano, basil, salt, and black pepper.
Reduce heat to low and simmer for 20-25 minutes, stirring occasionally. Remove from heat and set aside.
In a cast iron skillet (10-12 inches), heat the remaining 1 tablespoon olive oil over medium heat.
Add the Italian sausage, breaking it up with a spoon, and cook until browned and cooked through, about 7-8 minutes. Remove from heat and drain excess fat if necessary.
Preheat your oven to 425°F (220°C).
Punch down the risen dough and press it into the cast iron skillet, pushing it up the sides to create a thick crust.
Layer the shredded mozzarella evenly over the dough in the skillet.
Spread the cooked sausage evenly over the cheese layer.
Pour the tomato sauce over the sausage and cheese layers, spreading evenly.
Sprinkle the grated Parmesan cheese on top.
Bake the pizza in the preheated oven for 35-40 minutes until the crust is golden brown and the sauce is bubbly.
Remove from oven and let the pizza cool for 10 minutes before slicing and serving.