Begin by bringing a large pot of salted water to a boil while you cook the bacon.
In a large, cold, skillet with high sides, add the bacon then turn the heat to medium low. Slowly cook the bacon until it has rendered all of its fat and becomes crispy, about 10-15 minutes.
Remove the bacon and drain on a paper towel while you add the pasta to the water and cook according to package instructions. Remove all but 3 tablespoons of bacon grease from the pan.
Add onions to the skillet with the bacon grease and cook for 5 minutes, until translucent and soft. Once soft, add garlic and sage and cook for an additional minute.
Next, add the pumpkin puree and milk and stir to combine. Season with salt and pepper, then raise the heat to medium high. Add both cheeses and stir until melted.
Let the sauce bubble up and cook for 3-5 minutes, until thickened. Add the cooked pasta straight from the pot to allow a little pasta water to get into the sauce. Stir to combine and add more pasta water if needed. Add the bacon back to the pot and stir one more time.
Serve, topped with more parmesan cheese.