Add 1 cup of the veggie broth to a small saucepan and bring it to a boil. Turn off the heat and add the dried mushrooms, ½ teaspoon of thyme, and the 2 whole garlic cloves. Give it a stir, and let it sit for 15 minutes.
Heat a large pot over medium heat for a minute. Add the onions, and sauté for about 8 minutes, until they soften and start to brown, stirring frequently. Add a splash of water if they start to stick.
Add the sliced mushrooms, and sauté for about 8 more minutes, stirring often, until they have softened, adding splashes of water if they are sticking, and to pick up the brown bits that form on the bottom of the pan.
Transfer the broth with the rehydrated mushrooms, thyme and whole garlic cloves from the small saucepan to your high-speed blender, along with the cashews, and blend until smooth and there are no little bits of cashews left, about a minute.
To the large pot with the onions and mushrooms, add the remaining 3 cloves of minced garlic, 1/2 teaspoon of thyme, miso, salt, and the black pepper. Stir to combine, adding a splash or two of water to help dissolve the miso. Let this cook for a couple of minutes, while stirring.
Add 4 cups of the veggie broth and the dried mushroom powder to the pot, bring everything to a simmer, and then stir in the cashew mixture from your blender.
To a small bowl, add the arrowroot powder and the remaining 1 cup of broth, stir until the arrowroot is dissolved, and then add it to the large pot. Cook on medium heat for about 5 minutes, while stirring, until the Soup thickens. Don’t let it boil or you’ll lose the special healing powers of the miso! Now, it's ready.
Taste, and adjust the salt and pepper, and add another sprinkle of thyme if you’re feelin’ it. Serve your Cream of Mushroom Soup with crusty, whole grain bread or a batch of our Crunchy Croutons!
Arrowroot powder is made from a root vegetable—a tropical plant known as Maranta arundinacea—that is ground into a powder. It’s a great, healthy thickener for soups and sauces.