good tinned tomatoes, blended down to a paste, and then simmered to reduce on the hob.
That said, my favourite ‘pizza’ doesn’t have a tomato base, either:
Flammkuchen – a white cheese base with onions, lardons, maybe mushrooms
https://en.wikipedia.org/wiki/Flammekueche
and cheese* and caramelised onion marmalade
* blue, mozzarella, strong cheddar, goat…..whatever you fancy