Soak the cashews overnight until softened. If you're short on time, boil water and let cashews soak in hot water for 10 minutes. Once soaked, drain and rinse.
Add cashews, water, fresh lemon juice, apple cider vinegar, dijon mustard, and salt to a high-speed blender or food processor. Blend on high for 1-2 minutes, until smooth and creamy.
Enjoy immediately or let chill in the refrigerator for at least 1 hour.