Vegan soupsThe trick to making very flavorful stocks is to cook them long enough - even the classic mirepois (onion, carrot and celery) improves with cooking.
Try this stock: red onions, garlic, fresh ginger, parsley (or basil or cilantro, your choice), black pepper corns and a small bay leaf, filtered water, sesame oil, and lemon grass to finish. Make the proportions to your own liking; I use 5 or 6 large onions, a whole head of garlic, about 3 inches of ginger; two bunches of cilantro, and two stems of lemongrass to 4 quarts of water.
Heat the oil in your heaviest pan (I use my stainless steel stock pot), and saute the onions until they are deeply caramelized; put the garlic and ginger in the pot about half-way to molasses-dark onions. When the onions are ready, put the water, bay leaf and pepper corns in, bring it to a bare simmer, turn the heat down as low as it will go, and simmer as long as overnight. Put the crushed lemongrass and parsley in for the last hour or so of simmering. Strain the stock, cool, and store. You can put it in ice cube trays, freeze, then put in a zip-top freezer bag for later use.
Experiment with cooking time if you like - just make sure you get the onions brown enough - low and slow!
This also makes an excellent base for onion soup, it's especially good with rice noodles and a few fresh herbs to make a light soup.