Combine ingredients for meatball mixture: ground beef, milk, breadcrumbs, parsley, grated Parmigiano Reggiano, garlic salt, and egg. Mix until just incorporated. Do not overmix. Then set aside.
Heat a large saucepan on medium heat. Add in oil and onion. Saute onion for 5-7 minutes until slightly softened. Then add red pepper flake, and garlic. Saute another 2 minutes. Then add in crushed tomatoes, basil, salt, and sugar. Simmer for at least 20 minutes. Add salt and sugar to taste.
Meanwhile, shape meatballs into balls about 2 inches in diameter. Line a baking sheet and spread evenly with oil. Place meatballs on baking tray. Bake at 400 degrees F for 15 minutes, or until just cooked through.
Then add meatballs into the tomato sauce and allow to simmer at least 10 minutes. Top with grated Parmigiano Reggiano and serve with crusty bread.
