Fill a medium saucepan half full with water and place on stove over high heat. Add cauliflower, cashews, garlic, and onion. Boil for 15 minutes until cauliflower is VERY soft - should crumble easily when pierced with a fork.
Drain water and transfer the cauliflower, cashews, garlic and onion to a high speed blender. Meanwhile, fill the same medium sauce pan with water and cook pasta according to package instructions while you finish making sauce.
Add the remaining ingredients to the blender and blend on high until super smooth and creamy. Add more water if needed. Season to taste.
Drain cooked pasta, reserving 1/2 C of pasta water and set aside. Wipe out saucepan.
Pour blended Alfredo sauce into same medium saucepan and heat over low heat until it begins to thicken and get slightly “stretchy” (like melted cheese), stirring frequently, and adding pasta water little by little if needed.
Add cooked pasta back into the pan with alfredo sauce and toss to coat, adding more pasta water and heating through to achieve desired creaminess. Toss in parsley and serve hot topped with fresh cracked black pepper, reserving a little extra parsley for a finishing garnish.
*Reserve any leftover sauce in an airtight container to be stored in the fridge for up to 5 days or in the freezer for up to 6 months. Reheat on stove and toss with cooked pasta right before serving.*Miso Paste and Nutritional Yeast are what give this recipe its cheesy flavor! I have made it with just one or the other before, so feel free to do so, but the BEST flavor is achieved by using both.