Peel and cube the potatoes. Peel and chop the carrot. Peel and quarter the onion.
Add the vegetables to a large pot or Dutch oven of boiling salted water. Cover and simmer for 10 minutes, until the potatoes are fork-tender. Remove the boiled vegetables and save about 1 ½ cups of the cooking water.
Add the cashews, boiled vegetables, garlic powder, onion powder, salt, reserved cooking water, and nutritional yeast to a blender. Blend until smooth.
Pour the sauce over the macaroni and stir to coat.