Begin by pressing the tofu in between a folded towel, placing a heavy object on it for around 30 minutes. This will help excess water drain away from it.
Next, put the 6 cups of water on high on the stove, covered, to get the water boiling.
Start cutting your tofu by turning it on its side and making two cuts all the way through. Turn the tofu back on its flat side and make 4-5 cuts lengthwise. Turn the block again, being careful not to let any pieces slip away and then make another 5-6 cuts through the tofu until you have small bite-sized pieces.
While you wait for the water to boil, prep your veggies by washing and then cutting them up. Mushrooms should be sliced, spinach should be chopped, and scallions should also be chopped.
As water begins to boil, take a ladle full of water and drop a bouillon cube into it. Take a small whisk and carefully, over the boiling pot of water, stir into the water in the ladle until completely dissolved. Pour this back into the entire pot to disperse the flavors. Repeat this again with the second bouillon cube and then again with the miso.
Reduce heat to a simmer. After stirring the entire pot of soup, add in crushed garlic and cubed tofu until heated through, for a couple of minutes.
Last, add the vegetables and, stirring well, combine and simmer until vegetables are cooked to your liking, but no more than 5 minutes as vegetables can become overcooked and lose their taste and nutrients if boiled too long. Remove from heat and serve in a teacup along with your Japanese meal or enjoy by itself on a cold winter day.