Make the Meatballs:

Mix the Meatball Ingredients: In a large bowl, combine ground beef, breadcrumbs, Parmesan, garlic, egg, parsley, Italian seasoning, salt, and pepper. Mix until just combined; do not overmix.

Form the Meatballs: Roll the mixture into 1 1/2-inch balls (about 12-15 meatballs).

Cook the Meatballs: Heat olive oil in a large skillet over medium heat. Cook the meatballs in batches until browned on all sides. Remove and set aside.

Make the Sauce:

Sauté Aromatics: In the same skillet, heat olive oil and sauté the onion until translucent, about 3-4 minutes. Add the garlic and cook for another 30 seconds.

Simmer the Sauce: Add crushed tomatoes, Italian seasoning, salt, pepper, red pepper flakes (if using), and sugar. Stir to combine.

Add the Meatballs: Return the meatballs to the skillet, nestling them into the sauce. Cover and simmer on low heat for 20-25 minutes, stirring occasionally.

Cook the Pasta:

Boil the Spaghetti: While the sauce simmers, cook the spaghetti in a large pot of salted boiling water according to package instructions. Drain and set aside.

Serve:

Combine or Serve Separately: Toss the cooked spaghetti with the sauce and meatballs, or serve the spaghetti topped with sauce and meatballs.

Garnish: Sprinkle with additional Parmesan cheese and fresh basil leaves.