I worked in an Italian cafe as a student and the nonna taught me how to make tomato sauce (she called it sugo).
I got out of the way of making it and I can't get it right!
The process is definitely fry garlic in olive oil, add tinned tomatoes and fresh tomatoes, bring to boil, then simmer with the lid on until thick.
WHY is not working? It used to make a really thick, yummy sauce and this is too runny and not rich enough.