Whisk together egg yolk, lemon juice, mustard, water and salt until frothy.
Pour avocado oil in slowly while whisking constantly until the mayo begins to thicken. Once this happens you can add the oil in a thin stream, whisking until combined.
Keeps fresh for up to a week in the fridge and tastes best within a few days.
Notes
For Chipotle mayo - follow the mayo base recipe instructions above then add in: