Remove the roasted butternut squash from the oven and let cool slightly. Then, add 1 ½ cups of the roasted squash and the oat milk to a blender. Blend together until smooth and set aside for later.
Add the vegan butter to a saucepan and melt over medium heat. Once melted, add in the minced garlic and cook for 2-3 minutes until fragrant.
Pour the blended butternut squash into the saucepan along with the nutritional yeast, dijon mustard, and salt. Mix and cook together until smooth, about 1-2 minutes.
Mix the tapioca starch/flour and water together in a small bowl to create the slurry. Then, pour it into the pan and mix into the sauce ingredients.
Continue cooking the sauce, stirring consistently, for about 2 minutes until it begins to get a thick and stretchy consistency.
Remove the pan of butternut squash sauce from the heat and add in the cooked pasta and remaining roasted butternut squash.
Stir everything together and serve as is or top with fried sage. Enjoy!