Cut Roma tomatoes in half

Arrange tomatoes on an oven rack or tray, and add a drizzle of olive oil, and sprinkle of salt over each.

Roast tomatoes at 135 deg C for 2.5 - 3 hours(!)

Check the tomatoes after this time, they should almost feel like a jam or a jelly.

Put into a blender.

Add a splash of apple cider vinegar and some more salt

Add a little water, and check consistency as you go - it's less about the time, and more about the consistency - you want it to be as smooth as possible.