In a large bowl, combine ground beef, ground pork, breadcrumbs, grated Parmesan cheese, chopped parsley, a large egg, minced garlic, Italian seasoning, salt, and pepper. Mix gently until just combined.

Shape the mixture into meatballs about 1 inch in diameter, aiming for 20 to 24 meatballs total.

Heat 2 tablespoons of olive oil in a large skillet over medium heat. Add the meatballs in batches, browning for 5 to 7 minutes.

In the same skillet, add more olive oil if needed and sauté the diced onion, carrots, and celery for 5 to 7 minutes.

Pour in the chicken broth and diced tomatoes, bring to a boil, then reduce to a simmer for 10 minutes.

Carefully return the browned meatballs to the pot, simmer together for 10 to 15 minutes.

Add heavy cream and red pepper flakes, stir and simmer for another 10 minutes. Fold in the chopped spinach.

Ladle the soup into bowls and garnish with fresh basil before serving.