This is the vegetable peel stock that I learned to make in a Zen monastery kitchen. Nothing is wasted there. Onion skins, carrot tops, potato peelings, or any left overs from veggie prep, all... go into a large stock pot. When the pot is about full, it gets covered with water and simmered for an hour or so before being strained. This makes a good vegetable stock and is as simple and cheap as it gets. The only things to be careful of are either adding beet or chard trimmings- they may turn your stock pink, or adding too much of a strong tasting veggie like celery, rutabaga or celeriac.
Stud each onion half with two cloves. In a 7 or 8 quart stockpot put in the onion, garlic, bay leaf, peppercorns, and parsley along with all the veggie trimmings you have on hand. Add olive oil and enough water to cover the vegetables completely. Bring to a boil over a high heat. Cover and turn the heat down to low. Gently simmer for 1 hour.
Taste for salt, then strain the stock. Discard the soup vegetables. Use immediately or cool and bag and freeze.
For extra flavor, add a handful of dried shitake mushrooms or a bouquet garni .
Bag and freeze in quart size bags for later use in soups, stir fries, and stews etc.
1 quart/4 cups is the typically the amount sold in commercially boxed stocks and broths.