Squash and apples complement each other naturally; curry adds an exotic note. Feel free to experiment with other types of winter or summer squash.
Melt the butter in a pot. Add chopped onions and curry powder and cook, covered, over low heat until onions are tender, about 25 minutes.
Meanwhile peel the squash (about 3 lbs). A regular vegetable peeler works best. Scrape out the seeds and chop the flesh.
When the onions are tender, pour in the stock, add squash and the 2 apples (peeled, cored and chopped). Bring to a boil. Reduce heat and simmer, partially covered, until squash and apples are very tender, about 25 minutes.
Pour the soup through a strainer, reserving liquid, and transfer the solids to the bowl of a food processor fitted with a steel blade, or use a food mill fitted with a medium disk. Add 1 cup of the cooking stock and process until smooth.
Return the pureed soup to the pot and add apple juice and additional cooking liquid, about 2 cups, until the soup is of desired consistency.
Season to taste with salt and pepper, simmer briefly to blend and heat through. Shred Granny Smith apple, unpeeled. Serve soup immediately, garnished with shredded apple.