Add Tomatoes, garlic, oregano, basil, salt, and pepper to a blender and blend until smooth.
Transfer to a saucepan.
Add parsley, sugar, butter, and onion halves.
Simmer sauce for at least 20 minutes, longer if you have the time.
Meatballs can simmer in the sauce for extra flavor.
Be sure to taste to see if you need any extra seasonings.
Remove the onion before serving.