In a 3-quart saucepan, heat the olive oil over moderate 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 juice and bring to a boil, stirring often. Lower the heat and simmer for 30 minutes. Season with salt and serve. This sauce can be refrigerated for 1 week or frozen for 6 months.