Please forgive the shortness of the video, I recorded it with my phone and it tipped over before I was finished because of the immersion blender's vibrations on the countertop. But as you can see, it turned to mayo in just a few seconds. All I did to finish was to bring the immersion blender up to incorporate the oil sitting on top. So quick!
The most important thing to do is to use LIGHT olive oil. Regular extra virgin olive oil is to olive-y and strong, what you need is a really light oil so it doesn't give too much flavor. I would recommend a touch less salt, this was my first time using the Himalayan pink salt and this batch turned out a little more salty than expected. If you're following Whole30, you should use plain mustard or mustard powder because Dijon mustard has white wine, which is not Whole30-approved.
I've read that to make a smaller batch, you use just an egg yolk (save the white for your next omelet) and whatever amount of oil you want, like 1/4 to 1/2 cup. But I say go for a whole 1 cup batch, this stuff is so good! I eat it on everything these days.
And I follow the advice that it lasts longer than one week, in my book it should last for as long as your egg. I'm also using a farm-fresh egg that I bought at the farmers' market, really good quality.