Preheat your oven to 400°F (200°C).

In a large mixing bowl, combine ground beef, ground pork, kosher salt, freshly ground black pepper, finely chopped onion, large egg, chopped garlic, finely shredded Parmesan cheese, plain breadcrumbs, and fresh parsley. Mix until just combined.

Form the mixture into four large meatballs, each about the size of a baseball, and place them on a baking sheet lined with parchment paper.

In a large oven-safe baking dish, heat the olive oil over medium heat, add remaining chopped onions and garlic, and sauté for 3-4 minutes until fragrant.

Stir in crushed tomatoes, water, fresh basil leaves, dried oregano, salt, black pepper, and crushed red pepper flakes. Let simmer for a couple of minutes to thicken.

Nestle meatballs into the marinara sauce, cover with aluminum foil, and bake for 30 minutes. Remove foil and bake for an additional 20 minutes.

Let the meatballs rest for a few minutes before serving over cooked pasta and garnishing with finely grated Parmesan.