First, cut the "neck" sections from the bulb, and split each of those two pieces in half. Remove the seeds and pulp. Place the squash cut side down in a baking dish with a little water and cover with foil. Roast the squash in a 350 degree oven for about 30-45 minutes, or until the pieces are very soft. The "neck" portion will take longer, so if the bulb sections are done earlier those can be removed while the rest finishes cooking.
Meanwhile, chop the bacon into small pieces and begin to cook in your soup pot, over medium heat. Keep the heat low enough that the bacon does not get crispy. Once the fat has rendered and the bacon is still soft, turn the heat to medium-low and add the finely diced onion. Cook until the onion is very soft and begins to color.
Once the squash is done and cool enough to handle, remove the flesh from the roasted squash shell and add it to the bacon and onion mixture.
Add the stock (more or less depending on how thin you'd like your soup) and bring up to a boil. Reduce to a simmer, and cook for about 45 min - one hour.
After the timer goes off, pass it all through a food mill and discard solids. Or, you can blend or purée the soup and strain it. Stir in some heavy cream or more stock to thin it out, and top with minced fresh sage leaves. Serve warm.
