Combine cashews and garlic in a high-speed blender (such as Vitamix®); blend on high until cashews are reduced to crumbs, scraping down the sides of the blender in between blending. Add lemon juice and blend until well combined.
Add water, 1/4 cup at a time, and blend until the mixture has a smooth and almost thick consistency; mixture will thicken further in the fridge. Mix in nutritional yeast. Add the last 1/4 cup of water only if needed; do not exceed 1 1/2 cups water if possible. Mixture should be completely smooth with no lumps remaining.
Taste and add salt if needed. (The mixture will taste very lemony but will neutralize after 1 hour in the fridge.) Place in the fridge to thicken, about 1 hour.