In a soup pot over low heat, melt the butter.
Add the onion, salt, thyme, paprika, ginger, cinnamon and allspice. Cook 4-5 minutes, stirring occasionally, until the onion has softened.
Add the chestnuts, stirring to coat them with the spice mixture.
Add the stock and water, raise the heat to high.
Bring to a boil, then reduce to a simmer.
Simmer the soup for 30 minutes.
Using an immersion blender, puree the soup until smooth. If you do not have an immersion blender, carefully transfer the hot soup to a blender or food processor, and puree until smooth.
Adjust the seasoning as needed and serve immediately.