Heat a small, heavy-bottomed stock pot over medium heat; add the butter and let it melt; add the onions and a generous pinch of salt; stir well, cover, and reduce the heat to medium-low; continue cooking, stirring occasionally, until the onions are very soft and sweet (about 20 to 30 minutes); if the onions show any sign of browning, turn the heat down to low. Add the squash and just enough vegetable stock to barely cover the squash and onions; raise the heat to medium and cook until the squash is falling-apart tender. Add the cream and bring the soup to a boil; remove the soup from the heat; puree the soup as finely as possible and then pass through a fine chinois. Season the soup with the quatre épices and salt to taste; chill and refrigerate.
Serves 10 to 12.
