2 cups chopped onions
1/2 to 3/4 cup butter
2 green peppers, seeded and chopped
3 large celery stalks, chopped
2 cloves garlic, minced
1/2 pound fresh mushrooms, sliced
2 medium zucchini, chopped
12 large fresh tomatoes, peeled and chopped, or
    2 (28 ounce) cans whole tomatoes, chopped and not drained
1 (12 ounce) can tomato paste
1 tablespoon chopped fresh basil or 1 teaspoon dried basil
1/2 teaspoon thyme
1 tablespoon chopped fresh oregano or 1 teaspoon dried oregano
1 bay leaf
2 teaspoons salt, or to taste
Freshly-ground pepper, to taste