Baked Ziti with Ricotta: My Family's All-Time Favorite!

Ingredients

• 2 tablespoons olive oil (30 ml)
• 1 medium yellow onion, finely chopped (about 1 cup)
• 2 cloves garlic, minced
• 1 (28 ounce) can crushed tomatoes (794g)
• 1 (15 ounce) can tomato sauce (425g)
• 1 teaspoon dried oregano
• 1/2 teaspoon dried basil
• 1/4 teaspoon red pepper flakes (optional)
• 1/2 teaspoon salt
• 1/4 teaspoon black pepper
• 1 tablespoon granulated sugar
• 1 pound ziti pasta (454g)
• 15 ounces ricotta cheese (425g), whole milk or part-skim
• 1 large egg, lightly beaten
• 1/4 cup grated Parmesan cheese, plus extra for topping (approx. 30g)
• 1/4 teaspoon salt
• 1/8 teaspoon ground nutmeg (optional)
• 2 cups shredded mozzarella cheese, divided (approx. 225g)