Adapted from Food52 and The Essential New York Times Cookbook. I have made a double quantity here and have made a few minor adjustments: onion for shallot, no garnish, a bit more chicken stock...that's about it.
Heat a medium-size saucepan over low heat. Add the White Onion (1/2), Garlic (1 clove) and Water (1/2 Cup). Cook until the onions and garlic are softened, being careful not to let them burn, 5 to 7 minutes — the water will be nearly evaporated.
Add the Butternut Squash (8 cup) and the Chicken Stock (1 cup) and bring to a boil.
Reduce the heat, cover, and simmer until the squash is soft, about 20 minutes.
Using an immersion blender, purée until roughly smooth. (Alternatively, carefully pour the mixture into a blender. Holding the top down with a towel, blend until smooth.)
Add the Apple Cider (1 1/2 cup), Sour Cream (1/2 cup), Salt (1 teaspoon).
Continue blending until well combined. Add Freshly Ground Black Pepper (to taste) and add more salt if necessary. (I often add another teaspoon of kosher salt.) Add more sour cream if desired (I always do.). Thin out with more stock — you may need as much as another cup of stock. Taste, adjust seasoning again as necessary.