In a pot on medium heat, sautee onions with a little salt for around 10 minutes.
Add garlic and cook for 1 minute.
Add remaining ingredients. Bring to boil and reduce to simmer.
Cook sauce for 10 minutes with lid on. Then for another 10 minutes with the lid half on - to reduce liquid. Cook sauce for as long as you like, around 30 minutes things get magical.
Store in an airtight container in fridge for around 1 week. Or freeze for up to 3 months.