Roughly dice the fresh tomatoes, removing any hard cores, place them in a blender and puree until smooth and there are no longer and visible strips of skin.
Put the olive oil in a large, heavy-based pan over a medium-high heat. Add the garlic and fry for 2 minutes, stirring constantly to stop it from burning. Stir in the teaspoon of chilli flakes.
Pour in the blended tomatoes and stir. Cover, turn the heat to medium, and cook at a low bubbling simmer for 15 minutes - stirring every now and then.
Add in the salt, sugar, dried oregano and basil, as well as the freshly ground black pepper. Mix this into the tomatoes and cook uncovered for another 5 minutes until thickened.
If using, tear up the fresh basil leaves and stir them into the sauce.
Turn off the heat, taste for seasoning, and allow to cool.
Stored in a tightly sealed glass jar in the fridge, the pizza sauce will last for up to 2 weeks. Or seal it well and pop it in the freezer.
Notes
You can of course omit the chilli flakes if you're making this for young children, or alternatively 'turn-up' the heat and add more if that is your preference.
I like to stir in some fresh torn up basil at the end, but this is optional.