Add olive oil to a large soup pot or Dutch oven and heat over medium heat. Add the onions and sauté till soft and translucent, about 5 minutes.
Add the rosemary and garlic to the pot and stir for another 30 seconds, allowing them to release their fragrance.
Add the mushrooms and stir to coat. Let them sit undisturbed for about a minute, then stir them again and then let them sit for another minute. Season them with pepper and stir, letting them sit for another minute. Season with salt and continue to sauté until the mushrooms are tender, about three more minutes.
Next, add the balsamic vinegar and stir, allowing some of the vinegar aroma to evaporate.
Remove about ⅓ of the mushroom mixture to a blender along with the drained cashews, miso (or soy sauce), nutritional yeast, and two cups of the vegetable stock. Blend on high until completely smooth and creamy, about 30 seconds.
Add the mixture to the soup pot along with the remaining vegetable stock and cooked farro, and stir till well combined.
Bring the soup to a boil and let it simmer, uncovered, for about 10 minutes till slightly thickened. Add the kale and stir. Continue to simmer until the kale is wilted, about 3-4 minutes.
Taste and and adjust seasonings as desired. Serve hot and enjoy!