In a large bowl, combine the flour, cornmeal, salt, and yeast. Add in the cold, cubed butter and, using your fingertips, work it into the flour until the mixture resembles coarse crumbs. Gradually pour in the warm water while mixing until a dough forms. Knead the dough on a lightly floured surface until smooth, about 5-7 minutes. Cover with a tea towel and let it rise for 60 minutes in a warm, draft-free space.

Preheat the oven to 425°F / 220°C (200°C fan-forced). In a large skillet over medium heat, add the olive oil and sauté the onions and bell peppers until the onions are translucent, approximately 5 minutes. Add the sausage and cook, breaking it into pieces, until browned through. Drain any excess grease and set aside. In a separate bowl, stir together the crushed tomatoes, oregano, and dried basil.

Once the dough has risen, on a lightly floured surface, roll the dough out into a circle about 15-16 inches (38-40cm) in diameter. Grease a 14-inch (36cm) deep-dish pizza pan or a 12-inch (30cm) cast-iron skillet with olive oil. Note: a 12-inch skillet will produce a thicker pizza with a longer bake time — check for doneness at 35 minutes. Transfer the dough into the prepared pan, pressing it firmly into the bottom corners and up the sides to create a 2-inch (5cm) rim. Spread all of the shredded mozzarella cheese evenly over the dough base. Top with the cooked sausage, sautéed peppers, and onions in an even layer.

Pour the tomato sauce mixture over the filling, spreading it evenly. Sprinkle the top with grated Parmesan cheese. Drizzle with olive oil. Bake in the preheated oven for 30-35 minutes, or until the crust is deep golden brown, pulling slightly away from the sides of the pan, and the sauce is bubbling. Let cool in the pan for 10-15 minutes before slicing — this rest is essential for the layers to set so the slices hold together.