Boil your sweet potatoes, regular potatoes, and onions over the stove for about 15 minutes.
When they are so soft that you can easily poke a hole through them, remove them from the water and throw them in a food processor.
Add the of your ingredients to the food processor.
Make sure that you soak your cashews overnight in water before you make this. If you forget to do this overnight, you can soak them for about an hour in boiling water.
Blend all of your ingredients together in the food processor. I like my cheese sauce super thick, but if you feel like it's too thick for you, feel free to add a little bit of water or plant based milk.
Cook your pasta according to the package instructions.
Drain and rinse your pasta. Then pour your cheese sauce over it.
Notes
I like to top mine with chili flakes, basil, and some more nutritional yeast.