• Step 1: In a large bowl, combine the flour, salt, and sugar. Cut in the chilled butter until the mixture resembles coarse crumbs. Gradually add the ice water, mixing just until the dough comes together. Divide the dough in half, shape each half into a disk, wrap in plastic, and refrigerate for at least 1 hour (or up to 3 days).
• Step 2: In a large skillet, heat the olive oil over medium heat. Add the onion and garlic and cook, stirring occasionally, until softened, about 5 minutes. Add the Italian sausage and cook, breaking it up with a wooden spoon, until browned, about 8 minutes. Drain any excess fat.
• Step 3: Add the crushed tomatoes, oregano, basil, and red pepper flakes (if using) to the sausage mixture. Simmer, stirring occasionally, for 15 minutes to allow the flavors to meld. Remove from heat and set aside.
• Step 4: On a lightly floured surface, roll one disk of dough into a 13-inch circle. Carefully transfer the dough to a 9-inch deep-dish pie plate, pressing it into the bottom and up the sides to form a crust. Spread the sausage mixture evenly over the crust, then top with the mozzarella and Parmesan cheeses.
• Step 5: Roll the remaining dough disk into a 12-inch circle and place it over the top of the filled pie plate. Crimp the edges to seal, and cut several slits in the top to allow steam to escape. Bake at 400°F (200°C) for 30-35 minutes, or until the crust is golden brown and the cheese is melted and bubbly. Allow to cool for 10 minutes before slicing and serving.