Transfer the butternut squash, yellow onion, and garlic into a slow cooker.

In a separate large mixing bowl, combine the chicken stock, chipotle peppers, adobo sauce, and salt. Stir well, then pour the mix over top of the vegetables in the slow cooker.

Set the slow cooker to low, cover, and cook the ingredients for 6 hours.

Once cooked, transfer the soup into a blender (in batches) and pulse blend until smooth. Return the soup to the slow cooker (to keep it warm). Add additional salt and pepper to taste.

Ladle the soup into bowls and top with sour cream (optional). Serve.