Following is an easy, sustainable way to make it while reducing your garbage footprint in the ecology.
Step 1: Ingredients and Making Your Freezer More Efficient
Keep a large food safe plastic bowl with a lid in your freezer (a plastic freezer bag works too), and every time you prepare vegetables, throw the ends, peelings, onion skins and leftover bits in the bowl. When you have more of an herb than you can use before it goes bad, throw that in, too!
DONT throw in anything rotten, but do throw in anything that getting to old to use, but not actually rotten yet. The following list are some of the veggie bits I habitually throw in, and I'll also include a few thing that don't really work as a separate list:
Carrot ends and peelings
Scallion ends - including the root bits
Beet greens and peelings
Carrot greens (if you are of the school that eats them, not everyone is)
Stem ends of tomatoes
Onion ends and skins
Broccoli stems and leaves (also the trimmed yellowed florets if you left it in the fridge too long)
String bean strings and ends
Garlic paper and ends - also old garlic that is getting hard and yellowed but not when it gets powdery and mildewed.
Cucumber peelings IF they aren't waxed.
Lettuce stems and discarded leaves
Squash ends and rind if you peel that (zucchini, yellow, acorn, all of it!)
Leftover cilantro, dill, tarragon, basil, marjoram -any herbs
Leek trimming and ends
Pea pods if you shell your own
Parsnip ends and peels
Red or yellow pepper trimmings
Basically, the trimming, peelings and ends of nearly all vegetables.
Brassicas - cauliflower, Brussell sprouts and cabbage are not good, they add a strong, unpleasant odor and taste.
Anything that has gotten slimy or rotten - the idea is to toss it in the freezer bowl before it goes bad, but it's okay to use it just before it goes bad, when it's wilted, dried out, or yellowing.
Just keep throwing the trimmings into the bowl until it's full.
Step 2: Making the Stock
Throw in a bay leaf.
Put a lid on the pot, bring to a boil, then turn the heat down to simmer and simmer for at least 45 minutes to an hour. You want those trimmings to cook down to nearly mush.
Turn off the heat and let it cool for a while.
Put a colander or strainer in a large bowl, and pour the vegetables and stock through the colander into the bowl. Let drain through for a while, maybe 15 minutes to get all the liquid out. You can press the vegetable matter to drain it further, but that can bring out a bitterness with some of the vegetables, so usually let it drain on its own.
If your bowl isn't big enough, you may need to use two bowls, so the colander isn't sitting in stock too high to drain.
After the vegetable matter is well drained, it can go to the compost heap, or in the garbage, secure in the knowledge that you haven't wasted anything.
Step 3: Storage and Uses
It can then be kept in the fridge for a week, or frozen. I usually freeze some in ice cube trays, and in plastic bowls that hold one cup, then put the cubes in a plastic bag so I have measured amounts to hand when I need them.
I use the stock to cook pasta or rice, barley and other grains, to steam vegetables or dumplings, add salt to taste for vegetable broth, as a base for soups, sauces and stews, as a substitute for chicken broth if I'm cooking for vegetarian friends, and sometimes just reduce it ( cook on low heat uncovered until it loses half or more of its volume to concentrate the flavor) and use it as a sauce just like that. I've used it as a water substitute in bread stuffs, to add liquid when reheating leftovers. You can use it as a substitute for water in any dish that isn't sweet, and several that are!
I also melt stock I haven't yet used as a water substitute in making stock, for a richer stock. Stock that has been used to boil or steam vegetables can also be reused, provided it wasn't cooking brassicas like cabbage.