So, here's a primer on how to make a beautiful soup stock from almost nothing:
First, designate a spot in your freezer for a sturdy plastic box with a tight-fitting lid. If you don't have such a container, you can use a zip-type, gallon-size plastic bag.
Next, every time you prepare vegetables or meat, toss them in your stock box. Things that should go into the box: Butts, tips, and peelings of carrots, parsnips, turnips, and/or rutabagas. Butt ends of celery and garlic cloves. Leftover bits of green bell peppers (not the seeds). Outer layers of onions and shallots. Slightly wilted green tops of green onions, leeks, and celery. Potato peelings. Denuded chicken carcasses--cooked or not. Beef or lamb bones--cooked or not. Chicken skin. The yummy, meaty bits left over at the bottom of a roasting pan or frying pan, loosened up with a little boiling water, helped free of the pan with a little scraping from a stirring spoon. Leftover water from boiling or steaming veggies. Toss it all in the stock box, replace the lid, and put the whole shooting match back in the freezer.
What should NOT go in the box: Cruciferous vegetables, like broccoli and cauliflower, or dark green things, like spinach, kale, and chard. The first category will give the stock a noxious, "brassy" taste, while the dark green leafies will turn the stock nasty and swampish. Also, don't use fish scraps. (You can make a delightful fish stock, but that should be a different plastic box or bag entirely, into which you would tip onion, carrot, bell pepper, and pototato scraps, plus lots of fish bones and skin.)
When the stock box is full, take it out and set it in the fridge for half a day to loosen the frozen contents from the sides. If you're in a hurry, you can run very hot water over the outsides of the box, and the frozen block of scraps should slide out after a minute. DO NOT put the plastic box in the microwave to heat it up. (Health professionals suggest we use glass or microwave-able china to heat up our foods.)
Dump your collected scraps into a stock pot or a large sauce pan and cover everything with just enough fresh water so all the scraps are submerged. Here's my collection of scraps, just as they looked after dumping. I can see white and sweet potato peelings, celery hearts, bits of onion, carrot peelings, and some chicken carcasses:
Add some seasonings: a bay leaf or two, some thyme, a sprinkle of salt, some freshly ground black pepper. Here's what I added:
Cover and bring quickly to a full boil (this is an important step that kills off any pathogens that might've been lurking on your chicken or meat carcasses). Lower the heat and simmer for an hour or more, until the contents are pretty horrible-looking: limp and ugly and uniformly beige, kinda like this:
Ugh! But it smells really good by now.
Remove the hot pot from the stove and carefully strain the whole mess through a fine-mesh seive or colander into a clean container. I like doing this step in the sink to control splashes and so that I don't have to lift the heavy pot up so high. This lovely fine-mesh colander came from Williams-Sonoma:
If you know a lot of fatty things (chicken skin, roast beef scraps) went into your stockpot, carefully move the now-strained hot stock into the refrigerator. Let it cool uncovered overnight. The fat will rise to the top, and you can skim it off with a spoon and toss it. Either way, fatty or not-very-fatty, taste your stock to see how it's coming along. If it tastes rich and robust, congratulations! You're finished. You can use it immediatelly, or you can put the now-rendered stock into the freezer to keep for another day. (Just remember to label it so you know what is two months from now!)
If the stock tastes thin and watery, just pour it back into the stockpot and let it simmer for an hour or so more, uncovered, until it reduces in volume. This concentrates the flavor and renders it richer tasting. If you still aren't satisfied with the richness of the stock, you can add some powdered, cubed, or refrigerated bouillon to add a little depth to the stock. It's not cheating!
Here's what my stock looked like after being strained.
When you're ready to use your stock, put it in a clean soup pot, quickly bring it to a boil, drop it to a simmer, and then add whatever you want to make it into a lovely soup. This can be chopped bits of vegetables (more or less uniform sizes, please, for uniform cooking), a handful of uncooked rice, barley, or pasta. If you have cooked meat, add it in toward the last few minutes just long enough to heat it through. If you have cruciferous veggies (broccoli, cauliflower, Brussels sprouts), cook them separately and add them at the last few minutes just to heat through. Ditto with any spinach/kale/deep leafy greens. In about 20 minutes, all your raw veggies, rice, and pasta should be cooked through. Barley might take a little longer.
Here's a beautiful Scotch Broth I made out of my stock. I simmered a large handful of pearl barley and tossed in some pre-cooked meat left over from a pot roast. Scrumptious!