Heat the oil in a saucepan set over a medium–low heat. Add the onion, celery and carrot and season with the salt and some freshly ground black pepper to taste. Cover the pan and sweat the vegetables for 8–10 minutes, until soft but not coloured.
Add the garlic and cook, uncovered, for just 1 minute, until fragrant. Add the tomatoes and simmer for 3 minutes on a low heat.
Goodquality canned tomatoes don’t need to be cooked for very long, plus the longer you cook the sauce, the more water evaporates and the thicker it becomes, which isn’t the consistency that you want – pizza sauce should be thin but not watery.
Whizz the sauce with a handheld blender until smooth, or you could leave it a little chunkier if that’s what you prefer. Taste and check for seasoning – add a teaspoon of sugar if the tomatoes are too bitter or acidic.