Melt the butter in a large heavy saucepan over medium-high heat.
Add butternut squash, leeks, carrot, and celery; sauté until slightly softened, about 15 minutes.
Mix in the diced apples, thyme sprigs, and pinch of dried sage.
Add the chicken broth and 1 cup of apple cider then bring to boil.
Reduce the heat to medium-low, cover, and simmer until apples are tender, stirring occasionally, about 45 minutes. Cool slightly. Remove thyme sprig stems from the soup.
Purée soup with a handheld immersion blender (or in a blender) until creamy and smooth.
In a small saucepan over medium-high heat, boil the remaining 1/2 cup apple cider until reduced to 1/4 cup, about 7-10 minutes. Set aside to cool.
Place sour cream in a small bowl.
Whisk in reduced cider.
Ladle soup into bowls and drizzle with the cider cream and bacon crumbles, if desired. Enjoy!