Heat butter in a Dutch oven over medium heat. Add the shallots, garlic, sage and half the salt; season with pepper. Cook covered, stirring occasionally, until soft and fragrant, about 10 minutes.
Raise the heat to medium-high. Add the squash and the remaining salt, and continue to cook, stirring occasionally, until the butter begins to brown and the squash gets tender, about 10 minutes.
Add the cider and water and bring to a boil. Lower the heat and simmer, stirring occasionally, until the squash is very tender, about 20 minutes. Cool slightly.
Puree in a blender (or with an immersion blender) until very smooth. Return to pot and reheat over medium heat. Stir in vinegar and season with salt and pepper, to taste. Serve in warmed soup bowls with a dollop of creme fraiche and sage leaves on top.
This recipe has been updated and may differ from what was originally published or broadcast.