Melt the butter in a large pot (big enough to fit all the ingredients of the soup)
Add in the chopped onions, curry powder and cook until onions are tender.
While those are cooking, prep the squash by peeling, then cutting it in half and removing the seeds. Then chop into cubes.
When onions are tender, add in chicken stock, squash and chopped apple to the pot and bring to a boil. Reduce heat, cover partially and cook for about 20 minutes until squash is tender.
Pour the soup through a strainer, reserving liquids, then transfer the vegetables and solids to a food processor or blender.
Add one cup of reserved liquid and blend until smooth. You will use the reserved liquid later so keep it to the side.
Return the soup to the pot and add in the apple juice and 3 cups of the reserved liquid until desired consistency.
Season with salt and pepper and serve immediately with green apple slices to garnish.