How to Make It
Put water in pot to boil. If you're bothering to make dashi, throw in a few pieces of wakame, and simmer for about five minutes. If you're not using wakame, skip to the next step.
Once water is hot, add cubed soft tofu and simmer until everything is hot. Now would also be the time to add any vegetables that you have on hand.
Take the pot off the stove, and stir in miso paste. I recommend starting with about a tablespoon and a half, but feel free to add a little more or less, depending on how strong you want your soup and what kind of miso you're using. I personally prefer red miso, which has a stronger, funkier, and more fermented flavor, but if you like your miso on to mild side, give yellow a shot.
Pour the soup into a mug or a bowl or whatever vessel you have on hand, top with those thin slices of scallion if you're into it.