Heat the olive oil, onion, carrot, and celery in a large saucepan over medium heat. Cook until just translucent but not browned.
Add the tomatoes, salt, oregano, and sugar and simmer, partially covered, over low heat for 45 minutes, stirring occasionally.
This is our go-to tomato sauce for pasta and pizza. It's easy to change up; just a little alteration in herbs, kind of tomatoes or veggies and it's a different sauce. It goes with the Vegetarian Lasagna recipe.