This tastes so incredibly vibrant, this sauce--so rich and essential, as if all the tomatoes in the world have been distilled into one red tablespoon of platonic tomato-ness.
If I'm planning to freeze the sauce, I omit the herbs so that it can be used in either Italian or Mexican dishes without any conflicting flavors.
Try buttering your hot spaghetti before saucing; it adds so much delicious richness.
Heat the oven to 375.
Slice the tomatoes in half lengthwise, then arrange them cut-side down, in one layer on a large, rimmed baking sheet (mine is 12- by 17-inches), lined with parchment paper, if you like, for easier clean-up. Arrange the onions, garlic and herbs over the top, then drizzle the whole thing evenly with olive oil and sprinkle with salt, sugar, and pepper.
Bake for an hour and a half to two hours (or so), until the tomatoes are browning in spots and have fully collapsed. Around an hour in, the tomatoes will be sitting in a flood of juice in their pans, and then this juice will reduce as they cook further, which is what you want for a the thickest and most flavorful sauce.
Now you have two choices: put the contents of the pan (including all the juices), through a food mill: this will make a smooth, skinless and seedless sauce. Or else blend it all in a blender or food processor, which will make a good but more roughly textured and seedy sauce.
Use it or allow to cool completely and spoon into freezer bags and freeze.