One of the mother broths in Japanese vegetarian cooking is the kombu or kelp clear broth. It's a good broth to cook kabocha (pumpkin) in or make miso soup, vegan ramen broth or udon dashi. You can also add goodies and just use it as a clear broth soup.
It's pretty simple. Kombu (thick kelp that comes in a sheet) put in about 8-10 cups of cold water and 2 pieces of kombu. Put it in a glass container and let it sit for about 30 minutes, but I have left it in for half a day.
It's not heated because kombu has naturally occurring glutamates (like MSG) and it is heat sensitive. After about half an hour, take the konbu out and discard. The broth will keep for about a week in the refrigerator. If there is a white film at the bottom, it has spoiled and toss it.
For the clear broth, I took the kombu out and added dehydrated daikon (turnip), dried shiitake mushrooms and some wakame/hijiki. Once the broth heated up, I took the mushroom, daikon and larger pieces of wakame, rough chopped it, added frozen edamame and some tri-colored somen.
Eat like this with green onions or add about 1/4 cup miso dissolved in broth first and added in.