The best non-dairy buttermilk for sauces, dressings, and vegan versions of condiments like sour cream. Note that although no cooking is involved, you will need to prep ingredients at least an hour in advance (included in prep time). Serving size is 2 tablespoons.
Place the cashews in a bowl and cover with water by an inch. Let soak for at least one hour (two is better).
Drain the cashews (discard the water) and transfer to the jar of a high-speed blender (like a Vitamix or NutriBullet).
Add the fresh water, lemon juice, and salt, if using. Blend until smooth and creamy. Use immediately, or store in the fridge.
Notes
Technically, you don't need to soak the cashews to break them down in a mega blender like the Vitamix, but soaking them softens the nuts and produces a creamier result, imo.