In a heatproof medium bowl, add the cashews and cover them with the boiling water. Let them soak for 15 minutes but the longer, the better, up to 1 hour.
Drain the water from the nuts and place them in a blender. Add % cup cool water, the lemon juice, ½ teaspoon salt, and a few cracks of black pepper. Blend until smooth. Add more cool water, a tablespoon at a time, as needed to get to your preferred thickness. Taste and season with salt to taste. Store in the fridge for up to 2 weeks.