Garbage soup is one of my favorite, favorite things to make. It is immensely satisfying to create such yummy and healthy food out of stuff that would ordinarily be thrown out. (Especially if you live, as I do, where grocieries are ridiculously expensive.)
But the grocery bill is just one reason I routinely make soup out things other folks toss out as inedible, undesirable, or just plain tired. (Well, people who cook from time to time, anyway. If you live on takeout and microwaved frozen meals you won't be producing the basic ingredients for garbage soup in the first place.) True, I'm not producing a finished bowl of soup out of this stuff... but the base, a delicious homemade stock, is going into your kitchen garbage can, little bit by little bit, day after day. So why not collect the usable bits in a large ziplock bag in your freezer, as I do?
I don't use everything that ends up in the garbage can, of course, just what you might as well make soup out of: chicken, turkey, lamb, or beef bones; carrot peelings; the little bits around the stem ends of bell peppers and tomatoes after you've cut the rest off; parsley and cilantro stems; the leafy bits and root ends of celery stalks; wilted kale and swiss chard leaves; mushroom stems; the ends you slice off of zucchini, onions, shallots, even garlic cloves; the trimmings from bok choy, celery root, and fennel.
When the bag is full, on a day when you'll be home for a couple of hours, dump it out into your largest pot (no need to thaw first), cover with lots of filtered water, and set on the stove over medium heat. A scattering of whole peppercorns and, if you're feeling daring, a slice or two of fresh ginger root -- and maybe some fennel and/or cumin seeds while you're at it -- are useful for adding a little something extra. If you've got whole bay leaves in the house, toss in a few of those as well. Throw-caution-to-the-wind types might add a dried hot pepper pod or two, and three or four green cardamom pods.
When your pot comes to a boil, turn down the heat to maintain a healthy simmer and let it sit there, burbling happily to itself, for 90 minutes or more. If you want to feel involved, lift the lid from time to time and give the contents a stir, although that's really not necessary. If you've included meat or poultry bones, the stock is done when the joints disolve and the meat has fallen off the bone. Veggie-only stocks will be done sooner, although "done" is a very flexible concept here.
Take the pot off the heat and let it cool a bit with the lid off. If you've used meat or poultry bones it's a good idea to get the stuff into the fridge or freezer reasonably soon, but that doesn't mean you have to deal with it while it's still super hot. When it's cooled down a little, use a large strainer to scoop out most of the solids. Dump the contents of the icecube bin into your kitchen sink (drain plug in place) and fill the sink about half-full with water. Plunk the entire pot into the ice water and stir from time to time. It will cool down fast.
Now you can strain the stock into whatever you're going to keep it in and either freeze or refrigerate until you're ready to use it. Fat-phobics can refrigerate the stock overnight for easy fat removal before putting it into the freezer. (This is unlikely to be necessary unless you have included large quantities of chicken skin in the pot.) I suggest freezing some of your delicious homemade broth in 1-cup containers so you'll always have some on hand for braising, gravy, or to include in the liquid measure next time you cook rice or lentils or make mashed potatoes.
Having made your own garbage soup, the next time you see a recipe for stock in a cookbook, you'll have a good laugh. Sure, if you are trying to exactly duplicate a specific haute cuisine creation, you might want to do things "by the book." But that's not what we're after here; this is just plain old toss-what-you've-got-in-the-pot home cooking.
A few caveats:
1) Skip the broccoli, cauliflower, or cabbage trimmings; these veggies just don't taste good when boiled for a couple of hours
2) Potato, sweet potato, or winter squash make a cloudy, very sedimenty stock. If that will bother you, don't use them.
3) Keep an eye on your mix to make sure you haven't loaded it down with an excessive ratio of onion to everything else. Not that the result will be bad, exactly, but it will be intense. It's a good idea to collect enough carrot and celery bits, etc., to balance the onions.
4) An excess of kale, herbs, or other leafy greens will give the broth a greenish hue, and beets will turn it noticeably red. On the other hand, if have beets in the fridge you haven't gotten around to cooking because it seems like a hassle to boil them for an hour, go ahead and plop them in the stock pot, whole, next time you make garbage soup. Salvage them when you strain out the solids, or fish them out after an hour, whichever you feel inspired to do. The skins will slip right off, and the beets will be yummy for having been simmered with other delicious stuff.
To turn this base into a yummy soup, just add some each of:
Veggies: diced carrots and frozen peas (or snow peas in 1" pieces) are my favorites, but just about anything will do
Meat: diced cooked meat or chicken, or cubed tofu if you're vegetarian
Starch: cooked rice, barley, lentils, or pasta (you can also start by cooking the grains in lots of stock then add the other stuff when the grains are done).
Heat and serve.
I don't usually add salt to my soup or base stock. Instead, when serving, I first ladle a little of the broth into my bowl and stir in a spoonful (about 2 tsp) of miso before filling the bowl with soup.
Chicken soup is especially good with a dollop of plain or herbed yogurt stirred in. To make herbed yogurt, put about a half-cup of plain yogurt in your mini-food-processor and add whatever fresh herbs you have on hand (basil, parsley, and/or cilantro are obvious choices) and whiz it up. If you happen to have some cream or sour cream lurking in your fridge, a tablespoon or two of that added in is delicious, but not essential.