In a large pot, melt the butter. Add the onion, celery and garlic and cook over moderate heat, stirring, until softened, about 5 minutes. Add the white wine and simmer for 3 minutes. Add the stock and water and bring to a boil. Add the squash, cover partially and simmer over moderately low heat until tender, about 30 minutes.
Working in batches, puree the soup in a blender. Return the soup to the pot, bring to a simmer and season with salt, white pepper and nutmeg. Garnish with the pumpkin seeds, a drizzle of honey and the cucumber.