Here is the general formula for Vegetarian Soup Stock:
Save your veggie scraps in a large ziploc or other container in the freezer. If you are not using plastic, a glass bowl with a good covering will also work (a plate flipped over on top and tied works great).
As you go about your regular cooking, put all your scraps into that bag or bowl — onion skins, leek greens, carrots and carrot peelings, potato peels (as long as they are not green), sweet potato peels, pepper seeds (not hot peppers unless you like really spicy foods), tomato ends, etc.
When your container is full it's time to make soup! Yay for soup!
Take a big pot and pour your container full of veggie scraps in. It should almost fill the pot, with lots of spaces between all the veggies. Pour in enough water to fill the pot nearly to the top, with about one inch of clearance from the rim. Bring the water to a boil, then reduce it to a simmer, and simmer with the lid off for about 45 minutes to an hour.
You don't really need to stir this too much – just shift the veggies around once in a while, so that they all have a turn in the water. At the end of the simmering time, the water in the pot should have reduced by about a third. You can strain the stock from the veggies, toss the veggies into the compost heap, and the stock is ready to use.
OR you can leave the stock simmering on the stove, and add more water to bring it up to the top of the pot. Let it simmer down about 1/3 or 1/2, and then strain and use for stock. If you do this second reduction, it does increase the flavour.
One idea for soup for two people:
About 3 to 4 cups of the veggie stock
1 tomato, diced, or 1 small can of diced tomatoes with juice
Diced carrots, celery, leek, whatever veggies you have on hand
Frozen veggies (or fresh), about 1/4 cup of each: peas, corn, green beans
1 large potato, diced (alternately, you could use 1 cup of frozen hash browns)
1/4 cup Pearl or pot barley, optional (there is almost no conceivable difference – Pot barley has more fibre, and is generally more often used in soup. It's also sometimes cheaper)
OR 1/4 cup small pasta (like acini de pepe), 1/2 cup for larger pasta (small shells), also optional
Instructions:
Put the stock and tomatoes in a medium sized saucepan. Bring to a simmer. Add barley, if using, and simmer covered for about 30 minutes to cook the barley; add the hard veggies like carrots, leeks, potatoes, celery, green beans. Simmer, covered, for about 15 more minutes, then add frozen veggies, and simmer until heated through.
Enjoy!