You can either soak the cashews overnight in a bowl covered by a few inches of water or do the quick soak method. To quick soak, bring a small pot of water to a boil then remove from the heat and add the cashews. Allow to soak for 30 minutes then strain and rinse before using in the recipe.
Bring a small pot of water to a boil then add the diced potatoes and carrots. Boil for about 10 minutes, until the vegetables are fork tender. Strain the excess water and allow to cool.
Add the cooked vegetables, soaked cashews, nutritional yeast, garlic powder, onion powder, vinegar, lemon juice, salt and 3 tablespoons of water to the blender. Blend on high, scraping down the sides as needed or adding more water to help blend. I recommend adding just 1-2 tablespoons of water in between blending until the desired consistency is reached. It should be pourable but still thick and creamy. Taste test to see if you prefer more sour (vinegar/lemon juice) or more salt. Add more as desired and blend until smooth.
Serve cheese sauce warm or refrigerate in a sealed container for up to 1 week. Reheat in the microwave or on the stovetop when ready to serve. You may need to add a splash of water when reheating. Just be careful not to water it down.
I recommend using a high speed blender or something like a NutriBullet (this is what I use) for a smooth consistency. Using a food processor will work but the result will not be as smooth as what you see in the pictures.