In a large bowl, combine ground beef, 1/4 cup grated Parmesan cheese, breadcrumbs, 1 large egg, 2 cloves minced garlic, dried Italian seasoning, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Mix until just combined.
Form the mixture into 1-inch meatballs and set aside on a plate.
Heat olive oil in a large deep skillet or Dutch oven over medium heat.
Add the meatballs in batches and cook until browned on all sides, about 5 minutes. Remove meatballs from the skillet and set aside.
In the same skillet, add chopped onion and 3 cloves minced garlic. Sauté until onion is translucent, about 3 minutes.
Pour in crushed tomatoes and beef broth, stirring to combine.
Add dried spaghetti pasta, red pepper flakes, and season with salt and black pepper to taste.
Return the meatballs to the skillet, nestling them into the sauce and pasta.
Bring the mixture to a boil, then reduce heat to medium-low and cover.
Simmer for 15-20 minutes, stirring occasionally, until the pasta is cooked through and the sauce has thickened.
Stir in chopped fresh basil just before serving.
Serve hot, topped with additional grated Parmesan cheese.