Soak raw cashews in hot water for 2 hours or boil for 10 minutes, then drain.
Meanwhile, slice mushrooms, dice onion and mince garlic.
Heat up vegan butter in a large pot over medium heat. Add onion and garlic and sauté until fragrant.
Add mushrooms, season to taste with salt and pepper, and sauté until tender and golden brown.
Reserve about 1/3 of the mushrooms, and transfer everything else to a high-speed blender.
Add vegetable stock, soy milk, mushroom powder, nutritional yeast, vegemite and drained cashews to blender. Blend on high until completely smooth and creamy.
Transfer mixture back to pot and simmer for 5-10 minutes until piping hot. Stir in a splash of water to thin out the soup if it gets too thick.
Remove from heat and stir in balsamic vinegar. Taste and season with additional salt and pepper if necessary. Garnish with reserved mushrooms and parsley (if using). Serve hot with toasted bread. Enjoy!