Note that I don't normally measure out any of the following--I've made it so much now that I just throw stuff in, nothing has to be exact. If you're just learning, though, the amounts below are just right...
1Tablespoonlemon juice: the juice from one half lemon, or raw apple cider vinegar -- I prefer the lemon juice, but it definitely has a mild lemon twang to it, which I actually love the taste of. The vinegar has a twang, too, but maybe not quite as noticeable, in my opinion--experiment and see what you like. Use 1 Tablespoon for more flavor, or 1/2 Tablespoon if you want it very mild.
A squirt of regular or dijon type mustard, about 1 Tablespoon, which acts as an emulsifier with the eggs — if you're using the mayo in a recipe that a mustard flavor doesn't go well with, just use 1-2 Tablespoons of water. Or switch it up and use Dijon mustard sometimes!
Mix everything but the oil in a blender for about a minute. I like using my Bosch to make it hands-free. Readers have shared in the comments that they've had great success using their stick blenders in a small jar.
Add oil in very slowly, use the hole in the top of the blender if you have it. Within a few seconds you'll hear it start to thicken as you're blending. If it doesn't seem to be getting thick, just keep drizzling the oil in *very* slowly and it'll come together. (If it doesn't, see more about that below!) Once your oil is all blended in it's done, so fast!
Notes
***If your mayo flops (won't set up for the right consistency), see my information on this below the recipe! A note about the oil in this recipe: When I tried using no-flavor coconut oil, it separated after a night in the frig--bummer! And olive oils can be too strong tasting in this recipe. Avocado oil is just right.