Entirely Elizabeth

0 Grab a large wide-mouth jar and place the immersion blender in the jar. It should barely clear the sides and there shouldn't be much space between the two. Remove the immersion blender.
1 Add the egg, lemon juice, Dijon mustard, white vinegar, apple cider vinegar, and Celtic sea salt. Slowly pour the avocado oil on top and let it settle for a minute.
2 Place immersion blender in the jar and firmly press against the bottom. The egg should be right under and in the center of the immersion blender. 
3 Turn on the immersion blender and keep it pressed to the bottom of the jar until 1 inch of mayonnaise forms (about 10 to 15 seconds).
4 Slowly begin to move the immersion blender up and down to fully emulsify the ingredients into a smooth mayonnaise. (about 30 to 45 seconds). ELIZABETH'S NOTE: Be careful to not over emulsify the mayonnaise. It can become a thick jelly-like texture or even break (oil separates from the fat).
5 Turn off the immersion blender and remove it from the jar. Using a spoon, lightly stir the mayonnaise.
6 Place airtight lid on the jar (or place in a smaller jar) and store in the refrigerator.