Mel'S Brown Pizza Sauce - cooking recipe

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

Preparation

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.
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.
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.
Whisk oil and flour into tomato mixture until pizza sauce is smooth.