Tomato Sauce for Baccala

Place tomatoes in the jar of a blender or the bowl of a food processor; blend or process until pureed. Place olive oil in a large, heavy-bottomed saucepan over medium heat. Add onions and celery; cook until translucent. Add tomato puree, sugar, and salt; bring to a boil and immediately reduce to a simmer. Cook until thickened, 15 to 20 minutes.