In a large mixing bowl, combine the minced beef, finely chopped onion, minced garlic, egg, chopped parsley, panko breadcrumbs, salt, and cracked black pepper. Mix gently until just combined.

Form the mixture into meatballs, about 2 tablespoons each, and set aside.

Take each meatball, flatten it slightly, and place a cube of mozzarella in the center. Reshape the meat around the cheese, sealing it completely.

Heat olive oil in a skillet over medium-high heat and add the stuffed meatballs. Sear for 4-6 minutes until golden brown. Remove from the skillet.

In the same skillet, sauté onion and garlic until softened, then stir in the tomato paste and cook for an additional minute. Add risoni, chicken stock, passata, salt, and pepper. Simmer for 12 minutes, stirring occasionally.

Stir in grated Parmesan and fresh basil into the sauce. Add cooked meatballs back to the pan, cover, and simmer for an additional 3-5 minutes until cheese has melted.

Serve warm, garnishing with extra Parmesan and basil leaves.