Ingredients

• 4 onions, roughly chopped, or more to taste
• 3 stalks celery, roughly chopped
• 1 cup sliced fresh mushrooms (optional)
• 5 tablespoons minced garlic
• 3 (900 ml) cartons chicken broth, divided
• 3 (12 ounce) cans tomato paste
• 1/2 cup dried oregano
• 1/4 cup ground black pepper, or more to taste
• 1/4 cup white sugar
• 3 tablespoons celery salt
• 2 teaspoons basil
• 2 teaspoons onion powder
• 2 teaspoons seasoned salt
• 1 1/2 cups vegetable oil
• 1/2 cup all-purpose flour

Instructions

1. Working in batches, puree onions, celery, mushrooms, and garlic and 1/4 cup chicken broth in a food processor until smooth, adding more chicken broth as necessary.
2. Stir vegetable puree and remaining chicken broth together in large pot; bring to a boil, reduce heat to low, and simmer until flavors blend, about 45 minutes.
3. Stir tomato paste, oregano, black pepper, sugar, celery salt, basil, onion powder, and seasoned salt into broth mixture; bring to a boil, reduce heat to low, and simmer until flavors blend, about 45 minutes more.
4. Whisk oil and flour into tomato mixture until pizza sauce is smooth.