Simple to prepare, the secret of this marinara sauce is the simmering action that develops the flavors of the sauce, thanks to the aromatics and veggies that start the whole shindig rolling. Blended to a wonderfully smooth consistency, this sauce is slightly sweet and tart and silky and downright delicious.In a large pot, heat the oil over medium heat until hot and rippling. Add the onion and garlic and saute, stirring very frequently, until the onion is soft and translucent, about 3-4 minutes. Add the celery and carrots and season with salt and pepper. Cook, stirring frequently, until all the vegetables are slightly tender, about 5 minutes.