Prepare the vegetables. Peel and chop the onion, carrots, zucchini, and pumpkin. Cut the cauliflower into small florets.
Sauté the vegetables. Heat the butter or ghee in a large pot over medium heat. Add the onion, carrots, and zucchini and sauté for about 5–7 minutes, stirring occasionally.
Add the remaining vegetables. Add the pumpkin and cauliflower to the pot.
Add the liquid. Pour in the water or broth. Add the cream, salt, and black pepper.
Cook until tender. Bring the soup to a gentle boil, then reduce the heat and simmer until all the vegetables are completely tender, about 15–20 minutes.
Blend. Use an immersion blender to blend the soup until completely smooth and creamy. If using a countertop blender, blend in batches and use caution with the hot liquid.
Adjust the seasoning. Taste and add more salt or pepper if needed.
Serve. Ladle the hot soup into bowls and top with crispy croutons, pumpkin seeds, and freshly ground black pepper.