Up to two weeks ahead:
Make the herb butter -- Heat a small nonstick sauté pan over medium heat. When hot, add the shallots and heat to release their aroma and lightly toast them, about 30 seconds. Remove from the heat and add the sherry. Set the pan back on the heat and reduce the liquid to 2 Tbs., about 8 minutes. Let cool. In a small mixing bowl, blend the butter, chives, sherry-shallot mixture, salt, and pepper. Line a baking sheet with parchment or waxed paper and spread the butter 1/4 inch thick to cover about 8x6 inches. Cover and chill. With a small cookie cutter (I use a star) or a knife, cut out 12 small shapes. Wrap in plastic and freeze; freeze the remainder separately for the turkey.
Make the soup -- Put the leeks in a heavy-based nonaluminum, 8-qt. stockpot. Put the squash over the leeks; add the wine and broth. Cover and bring to a boil. Reduce to a simmer; cook until the squash is fork-tender, about 25 minutes. Let cool 15 minutes. Add the salt and pepper; purée in a blender (or food processor). Cover and freeze (or refrigerate up to 3 days).
On the day of serving:
Defrost the butter shapes. Reheat the soup over low to medium heat, stirring frequently (or in a microwave). To serve, ladle the hot soup into shallow bowls and garnish with herb butter and fresh chives.
nutrition information (per serving):
Photo: Ben Fink