if you are making a soup or a sauce from tomatoes roast the tomatoes in the oven until soft ( at about 180 ) .
Separate the pulp (for your sauce) from the skins, lay the skins on a tray in the oven (at it lowest temperature) until the are dried, it will take a couple of hours.
When dry and crispy allow to cool and then blend with salt, oregano and chilli flakes.
store in an airtight container and enjoy.