In a large bowl, combine the ground chuck, beaten egg, Parmesan, breadcrumbs, red pepper flakes, salt, black pepper, and Italian seasoning. Mix gently just until combined. Then roll the mixture into even 1 1/2-inch meatballs and set them aside.

Heat the olive oil and butter in a Dutch oven or large heavy pot over medium heat. Add the diced onion and cook until soft and translucent, stirring occasionally. Add the minced garlic and cook for about 30 seconds, just until fragrant.

Add the chicken broth, raw meatballs, crushed tomatoes, sugar water, chopped basil, Italian seasoning, salt, black pepper, bay leaves, oregano, and red pepper flakes. Bring the soup to a boil, then lower the heat to maintain a gentle simmer. Cook for 30 minutes. Browning the meatballs before adding them is optional.

Stir in the uncooked pasta and simmer for about 10 minutes, stirring occasionally, until it is al dente. Remove the bay leaves. Stir in the grated Parmesan and cook over low heat until the cheese melts and the broth thickens slightly. Taste and adjust the seasoning if needed.

Heat the broiler. Set oven-safe bowls on a rimmed baking sheet, then ladle the soup into the bowls. Top each serving with about 1/4 cup shredded cheese. Broil until the cheese is melted and bubbly, watching closely. Garnish with fresh basil, skim off excess grease if needed, and serve with toasted baguette slices.