Bring 4 cups of broth plus 2 cups of water to a boil and add the squash and carrots. Cook for 10-15 minutes or until fork tender. Drain, and transfer carrots and squash to the blender
. Add the onions, milk, nutritional yeast, garlic powder, onion powder, dijon mustard, salt and pepper and puree until completely smooth and creamy. This should yield about 4 cups sauce.