Deep cooked tomato kept herb- and chilli-free so it can move between Italian, Middle Eastern, Spanish and Mexican directions.
Heat oven to 150°C. Hand-crush tomatoes; reserve one can's worth for the end.
Add olive oil, butter, onion, carrot, garlic and salt; bring to a gentle simmer.
Cook uncovered in the oven 3–4 hours, folding the browned top in about hourly.
Discard carrot; discard or blend the onion. Stir in the reserved fresh tomato for brightness; blend or leave rustic.
Surface becomes deep brick red
Sauce reduces by roughly one third
Orange-red fat floats free and pools
No watery sharp tomato taste
Cool quickly. Freeze in 300–400 ml flat pucks or ~250 ml tubs. Fridge ~5 days; freezer ~3 months.
Good canned whole tomatoes are fine. If using local fresh/Roma tomatoes, cook longer because they are usually wetter.
Serious Eats slow-cooked tomato sauce + Marcella Hazan benchmark
Search: J. Kenji López-Alt Best Slow-Cooked Tomato Sauce