In a heavy saucepan over medium-low heat, cook the bacon until rendered and browned (it should still be soft, not too crispy).  Add the sage leaves and cook for approximately 2 minutes, until the sage leaves are crispy. Remove the bacon and the sage leaves with a slotted spoon and set aside.

Note: if skipping the bacon simply heat the oil and cook the sage leaves according to the directions above.

Using the same pan, add the onion and cook for 3-4 minutes or until the onion is soft and translucent. Add the garlic and cook for another 1-2 minutes until fragrant, stirring (add a bit of stock if the pan is browning and drying out). Add the butternut squash and the stock, stir, cover and simmer for approximately 20 minutes or until the squash is soft and cooked through.

While the squash cooks, bring a large pot of salted water to a boil for the pasta.  Add the pasta once the squash has finished cooking.

Transfer the squash mixture to a bowl and, using an immersion blender, blend until smooth. Be careful not to burn yourself! Place the squash mixture back into the pan and add the bacon (if using) and sage leaves (reserve a couple of sage leaves for garnish) along with the parmesan cheese and salt and pepper.

Using a set of tongs, add the pasta to the pan along with 1/2 cup of the pasta water. Mix together with the tongs, adding more pasta water if needed to make it a smooth, velvety sauce.

Serve immediately with the extra sage leaves and some extra fresh grated parmesan as garnish.