Use this time to clean, de-stem, and slice the mushrooms. Add them to the pan, along with the remaining salt, continuing to cook the onions and shallots for another 6 – 7 minutes. The edges of the mushrooms should be brown. This slower cooking technique will evaporate moisture, concentrating the flavors and caramelizing the sugars in the vegetables to lend extra depth to the sauce. Add the miso, breaking it up with a spatula. Cook for another minute.