Transfer the onion to the food processor together with the butternut, water, cashews, nutritional yeast, onion and garlic powders, mustard, salt and miso if using. Process on the hot liquid setting until silky smooth. Taste and adjust seasonings with salt and pepper.
1 lb butternut squash, 4 Tbsp nutritional yeast, 3/4 cup raw cashew pieces, 3 tsp onion powder, 3/4 tsp garlic powder, 2-3 tsp dijon mustard, 1.5 tsp sea salt, 2 tsp white miso paste, 1 cup water