Place a large saucepan over medium-high heat, add oil and then add the onions. Cook until the onions are soft and then add butternut squash cubes. Cook, stirring occasionally, until the squash is soft, about 10-15 minutes.
Add the chicken broth, brown sugar, parsley, sage, and White Truffle Salt and bring to a gentle boil. Reduce heat and cook on a low simmer for 10 minutes. Remove from heat and when the soup is cool enough to safely handle, remove the parsley and fresh sage, if you used it, from the soup and puree the soup in a blender. If a finer texture is desired, strain the pureed soup through a fine mesh strainer.
Pour the soup into a large saucepan. Season with additional White Truffle Salt, to taste. Heat to the desired serving temperature and serve with toasted pumpkin seeds and a dollop of sour cream/crème fraîche if desired.