Simple Vegetable Stock (Two Ways)

Name: Simple Vegetable Stock (Two Ways)
Prep time: 10 min
Cook time: 50 min
Total time: 1 h
Cuisine: American
Ingredients: 1 tablespoon olive oil (see note 1); 3 large onions (peeled and quartered, see note 2); 4 large carrots (peeled and cut into chunks); 6 large celery ribs ((stems), cut into chunks, see note 3); 6 cloves garlic (peeled); 1 bay leaf; 10 black peppercorns; 1 teaspoon salt (optional, see note 4); 8 cups water (2 quarts (2 liters)); fresh parsley (a bunch, see note 5)