Heat olive oil on medium-low heat in a large heavy pot. Sprinkle onions with salt and saute for about 10 minutes. You want the onions to be soft but not brown. Sprinkle flour into the pot over the onions, stir to mix and cook for about 3 minutes more (do not brown the flour mixture).

Use a grating blade in your food processor. Push the tomatoes through the processor tube and through the grating blade to make a rough puree. (I left my tomatoes a bit chunky.)

Stir tomatoes, sugar, garlic, herb bouquet, fennel, basil, saffron, coriander, orange peel and 1 teaspoon salt into the onion mixture. Cover and cook slowly for about ten minutes until the tomatoes give up their juices. Uncover and simmer for one hour. You want your sauce to be thick. Remove the herb bouquet and taste. Add salt, pepper, sugar and optional tomato paste. Stir.