In a Dutch oven over medium high heat, cook the bacon until crispy, about 15 minutes.
Remove the bacon, setting it aside on a paper towel to drain and leaving about 2 Tbsp of bacon fat in the pot.
Saute the onion in the bacon fat until softened, about 6 minutes. Add the squash, garlic, sage, salt and pepper and saute for 2 to 3 minutes more to brown the cubes lightly and draw out more flavor.
Add the stock, reduce the heat to low, cover and simmer for 10 to 15 minutes, until the squash is tender.
Meanwhile, cook the pasta, drain and set aside
Remove the squash mixture from the heat and pour in the milk. Using an immersion blender, puree the sauce. If you do not have an immersion blender, blend in batches in a regular blender. Taste and add more salt and pepper if needed
Add the pasta to the sauce and toss to coat. Chop the cooled bacon into bits. Serve the pasta with the bacon sprinkled on top