A few hours before you want to make this mayonnaise, take the egg and the mustard out of your refrigerator and place them on the counter.
Crack the egg right into the mini food processor, add salt, lemon juice, and mustard. Blend everything on high until lighter in color and almost foamy.
Using one of the holes in the lid, begin pouring the oil into the egg mixture while blending. If you don't have this particular mini food processor, you can simply pour the oil into the egg mixture in a very small stream, almost a drizzle. Once you have added about ¼ cup of oil, you will notice that everything has emulsified and you could pour the oil a bit faster.
You can enjoy this avocado mayonnaise right away but I find it tastes much better the next day. Letting it sit in the refrigerator for 12 to 24 hours really allows all the flavors to blend and develop!