Place cashews in a bowl of water (they should be completely submerged). Cover the bowl and allow cashews to soak at room temperature for 2-3 hours (not overnight). If your butternut squash isn't already cooked, you could use part of this time to cook it.
Drain cashews and place in a high speed blender with broth, butternut squash, garlic, salt, and pepper. Blend until completely smooth.
To serve warm, heat sauce in a small saucepan or skillet.
*Add more broth (or water) as necessary to achieve desired consistency.