In a skillet over medium-low heat, sauté 1 tbsp margarine and oyster mushrooms for 7 minutes, then set aside.
In a blender, grind cashews to a fine powder, then add 1 cup vegetable broth. Blend until completely smooth.
In a large stock pot over medium-high heat, add 1 tbsp margarine, onion, cauliflower, and garlic. Sauté for 5 minutes, then add bay leaves, thyme, white pepper, remaining vegetable broth, cashew mixture, and salt. Bring to a boil and then reduce to low heat and cook for 15 minutes. Remove bay leaves.
Using either an immersion blender or regular blender, blend until completely smooth. Add potatoes and cook over low heat for 40 minutes. Stir in the mushrooms. Serve hot.