You'll need an immersion blender for this recipe.

1. In a pint sized mason jar (you'll need a tall narrow container like a jar or a glass), add the egg yolk, lemon juice, water and dijon mustard.
2. Measure out 1 cup of avocado oil and add it to the jar. Usually mayo recipes require you to add the oil to a blender after you've begun mixing, but this is not necessary with an immersion blender and a tall container (trust me, I've done it many times!).
3. The oil will naturally separate from the acidic ingredients at the bottom. Place the immersion blender all the way down to the bottom of the container before turning it on.
4. Then, turn on the immersion blender and keep it at the bottom. You will begin to see the mayo forming on the bottom, once the white mayo starts working it's way up the sides (after about 30 seconds or so) start to bring the immersion blender up to incorporate more of the oil at the top. Once the everything is mixed, you've got mayo! Now just add salt and blend for a few seconds more to mix.