Place tomatoes, garlic and onions in shallow roasting pan. Drizzle with olive oil and salt, pepper. Toss with herbs and place in 400 degree oven.
Stir tomato mixture every 20 minutes and allow to roast until edges are browned and liquid is reduced somewhat. It will take about an hour or so.
Remove from oven and allow to cool.
Place everything in a bowl or food processor and squeeze out garlic cloves.
Remove the stems from the herbs. Puree the mixture using an immersion blender or food processor. Taste and adjust seasoning with salt, pepper and/or a pinch of sugar.
Add torn basil if desired.
Sauce freezes beautifully.