1. Pre-heat oven to 350 degrees F. Peel the butternut squash, remove the seeds, and cut into 1-inch cubes. Place in a lightly oiled roasting pan and bake for about 30 minutes or until fork tender.
2. Place 2 cups of the cooked squash into a blender. Set the rest of the squash aside for the pasta.
3. Heat a large skillet over medium-high heat. Once hot, add oil, garlic, mushrooms, rosemary, and red pepper flake (if using). Season with a pinch each of salt and pepper and stir.
4. Sauté for 3-4 minutes, stirring frequently, until the mushrooms are slightly browned. Then mix in the kale and the cooked butternut squash that was set aside. Reduce the heat on the skillet to low.
5. Bring a large pot of water to a boil and season generously with salt. Add the penne and cook according to package instructions, then drain (reserve 1-2 cups of the cooking liquid) and add the penne to the skillet with the vegetables.
6. While the pasta is boiling, make the sauce: To the blender with the 2 cups of cooked butternut, add coconut milk, nutritional yeast, ground sage, garlic powder and another pinch of salt and black pepper. Blend until creamy and smooth, adding in some of the reserved pasta water or coconut milk if the sauce becomes too thick.
7. Pour the sauce over the vegetables and pasta in the skillet and heat through. Add more reserved pasta water if needed to achieve desired consistency. Taste and adjust salt to your liking.