Place egg in the bottom of a mason jar or large glass. (must hold at least 1 pint). Do not mix the egg
add apple cider vinegar, lemon juice, mustard and salt
Pour oil on top of egg and vinegar. Try not to mix the ingredients, they should layer
Gently place the immersion blender into the jar and trap the egg underneath.
Start the blender on low, without moving the blender around and have the egg begin to emulsify in the oil then speed the blender up a little
As the mixture begins to emulsify, gently move the blender up and down, trying not to take it out of the mixture.
Once the mixture is mostly mixed, turn off the blender, lift it out and gently push back down to get the remaining oil to the bottom.
Start the blender again to finish mixing.
Place lid on jar and store in refrigerator for up to 10 days.
If your mayo separates, you can place an egg yolk in the bottom of a jar and beat it and then slowly add the mayo. That will re-emulsify the mayonnaise.