Place the stock, cashews, garlic clove, onion, nutritional yeast, and miso paste into the Vitamix container and secure the lid. Start the blender on its lowest speed, then quickly increase to its highest speed. Blend for 5 minutes 45 seconds, or select Hot Soups program and allow the machine to complete the programmed cycle. In a large bowl, combine the cooked pasta and mushrooms, parsley, lemon juice, black pepper, and blended sauce. Stir well to incorporate, and serve after a moment or two when sauce begins to thicken.