To ramp up heartiness but not fat or calories, purée half the batch in a blender, then stir it back into the pot.Tomatoes are more nutritious cooked than raw, because heat increases the amount of lycopene you absorb.
Put the oil in a large pot over medium heat. When it's hot, add the onion and carrot, sprinkle with salt and pepper, and cook, stirring, until the vegetables begin to soften (3-5 minutes). Add the tomato paste, lower the heat a bit, and continue to cook, stirring to coat the vegetables with the paste, until the paste begins to darken--don't let it burn (1-2 minutes).
Strip the thyme leaves from the stem and add them to the pot along with the tomatoes. Cook, stirring occasionally, until the tomatoes break down (10-15 minutes). Add 2 cups of the water or juice and bring to a boil, then adjust the heat so that the mixture bubbles gently. Let cook until the flavors meld (5 more minutes).
Taste and adjust the seasoning; if the soup tastes flat (but salty enough), stir in the sugar. If it's too thick, add more water, 1/4 cup at a time. If it's too thin, cook until it thickens and reduces slightly (this will also intensify the flavors). Garnish with basil, if using, and serve.
Change It Up!
Hearty Tomato Soup: Add 1/2 cup white rice, bulgur, or couscous with the water in Step 2, along with 1 more cup liquid. Cook until the grain is tender (5-15 minutes) and be prepared to add a little more water if the soup gets too thick.
Spiced Tomato Soup: Instead of the fresh thyme and basil, add 1 TBSP curry or chili powder or 1 tsp smoked paprika (pimentón) along with the tomato paste in Step