1You can grill or roast the tomatoes, which I recommend, to add a smoky flavor. Heat large sauce pan on med-high heat, add olive oil and onion and cook onions until tender, but not browned, 5-10 minutes.
2Add chopped tomatoes, stir and reduce to simmer. Simmer until the tomatoes are covered in their own liquid, about 25 minutes. Remove from heat and puree soup in batches. A blender works best.
3Return soup to pan, add salt and pepper, stir, heat through and serve.