Add in the egg, mustard, vinegar, lemon juice, and salt.
Blend using an immersion blender for a few minutes until all of the ingredients are mixed well and mayo is thick. Start at the bottom of the mixture and work your way up.
Store in the fridge. Mayo will last 2-3 weeks before it starts separating.
Video
Notes
*Mustard- I prefer dijon but you can use yellow or stone ground mustard.
**Vinegar- I use apple cider vinegar but you can use white vinegar.