This is my favorite miso recipe.
Slice all the onions into thin rings, and chop the garlic. Melt the butter over medium heat, and add the onion & garlic, pepper and salt. Stir occasionally and continue cooking ubtil the onions are "scummy". This is important, because if you try to shortcut, the flavour suffers. At this point, add 10-12 cups of water, until the stuff looks "soupish", the colour is light brown, and the onions are swimming around. Then add 2-3 tbsp. of tamari. Turn up the heat, and when the soup is warm, take some of the liquid out, and dissolve the miso in it. Stir it back in and heat to serving temperature. I've heard that boiling miso destroys its goodness, does anyone know any more about that?
The way I usually eat it is to put cheese on a piece of garlic toast in the bottom of the bowl before I pour the soup in.