Add the cashews to a heatproof bowl and cover with hot water by a few inches. Set aside to soak for 20 minutes.
Drain the water and add the soaked cashews to a small blender* with the avocado, cilantro, lime juice (starting with the lesser amount), garlic, salt, and water (starting with the lesser amount). Blend until creamy and smooth, adding more water 1-2 tablespoons (15-30 ml) at a time as needed to encourage blending.
Taste and adjust as needed, adding more salt to taste, lime juice for tanginess, or garlic for zing.
Best when fresh. Leftover sauce will keep in a sealed container in the refrigerator for 1-2 days, but the color will become darker. Not freezer friendly.
Video
Notes
*We tested this recipe in both a Nutribullet and Vitamix 5200 (this model has a narrow base) and both worked well. *Adapted from our Sweet Potato Black Bean Enchiladas. *Prep time includes soaking cashews. *Nutrition information is a rough estimate.