In a 3-quart saucepan, heat the olive oil over medium heat. Add the onion and garlic, and cook until soft and light golden brown, 8 to 10 minutes. Add the thyme and carrot, and cook 5 minutes more, until the carrot is quite soft. Add the tomatoes and reserved juice, and bring to a boil, stirring often. Lower the heat, and simmer for 30 minutes until thick. Season with salt. The sauce can be stored in the refrigerator for 1 week or up to 6 months in the freezer.