1. Place cashews in a large bowl and cover with cool water by 1 inch. Cover and refrigerate for at least 4 hours.
2. Bring 1 cup fresh water to a simmer. Drain cashews; rinse with cool water. Transfer to a food processor or high-speed blender. Add half of simmering water, lemon juice and salt to processor; process until smooth. Add more simmering water 2 tbsp at a time until mixture has a thick sauce consistency.