Add the sliced mushrooms, tamari, dried herbs and a few tablespoons of water to a medium pot and sauté for 8 to 10 minutes, stirring occasionally until the mushrooms release their juices and start to brown. Remove 1/3 cup of the mushrooms from the pot and set aside.

Add the onion and garlic to the pot of mushrooms and sauté again for another 8 minutes until the onions become translucent. Stirring often and adding water as needed to prevent burning. Add the red wine vinegar, stir and set aside.

Drain the cashews, discard the soaking liquid and add them to a blender along with the mushroom/onion mix, vegetable broth, nutritional yeast, and miso and blend on high until smooth.

Transfer back to the pot and bring to a gentle simmer. Taste and season with salt and pepper. Add more broth to thin the soup is desired. Divide among bowls and garnish with reserved sautéed mushrooms, a drizzle of tahini, and/or red pepper flakes.