Add aquafaba, mustard and salt to a blender or stand mixer.
While the blender/mixer is running, very slowly drizzle in the oil (this step should take around five minutes).* Then very slowly add the apple cider vinegar and lemon juice. Taste and adjust seasoning, if needed.
Transfer the mayonnaise to a jar and store in the refrigerator for up to a week.
*Make sure you take your time drizzling in the oil because if you add it too quickly the mixture will separate and be ruined.
Nutritional information is to be used as a guide only as calories and nutrition vary between products and brands worldwide.