Baked Ziti With Ricotta From Rossella Rago - Appetito

Ingredients

• 2 tablespoons extra- virgin olive oil
• 1 small onion, diced into 1/4-inch pieces
• 1 25-ounce jar tomato purée or 1 28-ounce can crushed tomatoes
• water to rinse jar or can
• 1 teaspoon salt
• 4-5 fresh basil leaves, torn
• 1-1/4 cup whole-milk ricotta cheese
• salt for cooking
• 1 pound dried ziti
• 8 ounces fresh mozzarella, diced into 1/2-inch pieces
• 1/2 cup grated Parmigiano- Reggiano, divided