Preheat oven to 250°.
Place tomatoes in glass Pyrex dish.
Season generously with salt.
Add a few good glugs of olive oil.
Shake dish to coat.
Roast in preheated oven for approximately 3 hours until blistered and caramelized. Don't be afraid to roast them so that a jam like consistency is reached. Using enough olive oil is the key to achieving this, just a few glugs is all you need.
If there are any leftovers, store them in a glass Tupperware in your refrigerator for up to a week.