Quarter the mushrooms and dice the potatoes, onion, and cauliflower into similar-sized pieces.
Melt the butter in a large pot over medium heat.
Add the potatoes and onion. Cook until lightly golden, about 5–7 minutes.
Add the mushrooms and cook for 2 minutes.
Add the cauliflower and cook for another 2–3 minutes.
Pour in the water and bring to a boil.
Reduce heat and simmer for 10–15 minutes until the vegetables are tender.
Blend the soup until smooth using an immersion blender.
Reduce heat to low and stir in the heavy cream, cream cheese, and salt.
Continue stirring until the cream cheese has completely dissolved.
Add the shredded cheese and stir until melted.
Season with black pepper and serve hot.