Kabocha is a type of winter squash commonly used in Japanese and Thai cuisine that is becoming more common in supermarket aisles today. Here, it is used similarly to butternut squash to make a simple and delicious puréed soup.
Using a large knife, carefully split the squash in half and remove the seeds. With a peeler, carefully remove the skin. (It is important to remove all of the green, as the skin is extremely bitter.) Chop into 2-inch pieces.
In a large, heavy-bottomed stockpot over medium-high heat, add the butter and cook until it is browned. (For this soup, it is important the butter browns, as it adds a nutlike flavor.) Add the onions and cook until translucent, stirring occasionally. Add the white wine and simmer for 5 minutes. Continue by adding the kabocha squash and chicken stock. Bring to a boil. Reduce heat to medium and let simmer for about 20 minutes or until the squash pieces are soft. Add the heavy cream and bring back to a simmer. Remove from heat.
In a blender, blend the soup in small batches until smooth. Pour the blended soup through a fine sieve into a clean stockpot. Return the soup to medium-high heat and whisk in the butter and brown sugar until combined. Taste and adjust seasoning with salt and white pepper. Keep hot until ready to serve.
Ladle the soup into individual soup bowls and garnish with crème fraîche and freshly grated nutmeg. Serve immediately.