01 - Combine ground beef, breadcrumbs, Parmesan, milk, egg, garlic, onion, parsley, oregano, salt, and pepper in a large bowl. Mix gently until just combined to avoid overworking the mixture.
02 - Form the mixture into 16 to 18 meatballs, approximately 1.5 inches in diameter each.
03 - Heat 2 tablespoons olive oil in a large skillet over medium heat. Add meatballs in batches and brown evenly on all sides, about 5 to 7 minutes total. Transfer browned meatballs to a plate.
04 - In a large saucepan, heat 2 tablespoons olive oil over medium heat. Sauté onion until translucent, about 3 to 4 minutes. Add garlic and cook for 30 seconds until fragrant.
05 - Add crushed tomatoes, dried basil, oregano, red pepper flakes if using, sugar, salt, and pepper to the saucepan. Stir well and bring the sauce to a gentle simmer.
06 - Return the browned meatballs to the simmering sauce. Cover and cook gently for 20 to 25 minutes, turning meatballs occasionally, until fully cooked and sauce thickens.
07 - Adjust seasoning to taste. Garnish with fresh basil or parsley. Serve hot over cooked pasta or accompany with crusty bread.