Add the cauliflower, onion, garlic and water to a pot, bring to a boil and turn heat down to low, cover for 10 minutes until cauliflower is very tender.
When done cooking, add the mixture to a blender along with the cashews, broth/milk, miso, and seasonings. Let cool a bit so the heat doesn't blow the top off the blender. :) Blend for a full minute, scrape down the sides of container and blend for another 30 seconds. It should be thick and creamy.
Use this as a white sauce for noodles, over root vegetables to make a scalloped casserole, in a squash lasagna or to make creamed greens.
For a gravy, slice and sauté mushrooms and another 1/2 cup of chopped onions, and pour this sauce into the pan once the mushrooms have cooked and lost most of their moisture. Use the gravy over grains, cooked with lentils, on top of veggie burgers or as a Rague with kale, chard and collard greens.