Grease a 13″ x 9″ baking dish with 1 tbsp. garlic olive oil.
Place the cut up butternut squash in a large sauce pot of hot water and bring to a simmer. Simmer for approximately 15 or until the squash is fork tender. Drain and reserve.
Bring a large stock pot of salted water to a full boil. Add the pasta and cook based on the package instructions to al dente.
In a large stock pot, heat 4 tbsps garlic olive oil over medium heat. Add the shallot and sauté for about 2 minutes until the shallot just begins to turn golden.
Add the flour into the olive oil and whisk to blend thoroughly for about one minute, stirring constantly. Slowly pour the milk into the flour roux, whisking constantly. Add the cream and continue whisking until thickened. This is your béchamel sauce. Whisk until there are no lumps and the texture is creamy and smooth.
Take 1 cup of the béchamel from the pot and add it to a blender or food processor with the butternut squash. Process until smooth. Add the butternut squash mixture back into the pot with the rest of the béchamel. And whisk to combine. Add all of the cheese to the béchamel, reserving 1 cup of gruyere cheese. Stir to melt and combine. Taste for seasoning and adjust with salt and pepper if desired.
Add the truffle oil (optional), and the pasta. Mix well and pour into the prepared baking dish. Top with the reserved cheese, and bake for 25 minutes until the top is golden brown and the pasta bubbly.