Melt the butter in a medium stockpot or dutch oven over medium-low heat. Add the leeks, carrots and garlic, sweat, stirring occasionally, until softened and lightly browned, about 5 minutes.
Add the butternut squash, nutmeg, salt and pepper, and cook, stirring occasionally, for another 5 minutes.
Add the sherry to the pan and cook for 2-3 minutes, or until reduced slightly, then add enough stock to just cover the vegetables. If 3 cups isn't sufficient, make up the difference with water.
Turn the heat up and bring to a boil. Then reduce the heat to simmer, and simmer uncovered for about 20 minutes, or until the squash is fork-tender. Using an immersion blender, blend until smooth.
Add heavy cream, half the parmesan and sour cream blend until well incorporated using the immersion blender.
Transfer back to sauce pan and return to heat, add bacon and parmesan cheese reserving some for garnish. Add more chicken broth if necessary to reach desired consistence.
Heat to desired temperature.
Ladle into bowls and drizzle with sherry, cream and sprinkle with parmesan cheese.
