Drizzle with olive oil, season generously with salt and pepper, and toss. Roast for 40 minutes, tossing halfway through.
While the squash is roasting, heat the butter in a large dutch oven or soup pot over medium-low heat. Once the butter is melted, add the onion, garlic, sage, salt, ginger, nutmeg and cayenne. Cook until the onions are translucent and the garlic and spices are fragrant.
Deglaze pan with ½ cup of the chicken stock, scraping up and mixing in any bits that are stuck to the bottom of the pan. Transfer the onion mixture, with the liquid to a high-powered blender. When the squash is finished roasted, add the squash and the remaining chicken stock to the blender with the onions and puree until smooth.
Increase the heat in the pan to medium-high and cook the sausage. Once it is browned, drain the excess grease. Pour the pureed squash back into the pan with the sausage.
Mix in the half and half, taste and add more salt and pepper if needed. Cook on medium for 10 minutes, stirring frequently,
Then reduce heat to low and let simmer 30 minutes.
Top with sour cream, fried sage, and pepitas before serving, if using.