Prepare Soffritto: Blend sliced celery, carrot, onion, garlic, a drizzle of EVOO, and a splash of water, until thick and creamy, then set aside.
Mix Meat: In a large bowl, mix ground pork and beef mince using your hands.
Prepare Bread: Soak the bread in water, squeeze out the excess liquid and tear into small pieces. Add to the meat mixture.
Combine Ingredients: Add dried herbs, half of the soffritto, breadcrumbs, cheese, salt, pepper, and egg to the meat mixture. Mix until smooth.
Shape Meatballs: Wet your hands and form the meat mixture into meatballs. Place on a tray lined with parchment paper.
Make the Sauce: In a deep pot, cook the remaining soffritto in EVOO. Add water and cook for 10 minutes. Add tomato passata, stir, cover, and simmer for 1 hour.
Cook Meatballs in Sauce: Drop meatballs into boiling sauce one at a time. Cover and cook for 30-40 minutes on low heat.
Serve: Tear fresh basil leaves over the cooked meatballs and sauce. Serve with a generous amount of sauce and basil on top.