In a 4 quart saucepan, combine the onion, potato, cashews, ginger and stock. Bring to a boil, then reduce to a high simmer and cook, partially covered and stirring once or twice, for about 10 minutes or until the onions have begun to soften.
Add the apple to the soup. Continue to cook until the apples have softened, about 5 to 8 minutes.
Next, add the trimmed broccoli to the soup and cook, monitoring closely, until the broccoli is tender, but the color is still vibrant green. Immediately remove the soup from the heat and stir in the salt and white pepper.
As soon as the soup is cool enough to handle, drain the vegetables out of the soup broth, allowing the broth to collect in a mixing bowl. Transfer the vegetables to a blender and puree, adding enough water to facilitate the process, until the soup is evenly pureed. Stir in enough reserved soup broth to achieve the soup texture you desire. Taste and adjust the seasonings.
If you have a great deal of broth left, you can reduce the remaining broth over high heat, then add it in a more concentrated form. If you’ve cooked the soup over higher heat you probably won’t have much broth left, so no need to reduce, simply add.
The soup may be eaten immediately or prepared up to 5 days in advance. Serve piping hot with red pepper flakes on the side as a garnish.